gh-108303: Create Lib/test/test_dataclasses/ directory (#108978)

Move test_dataclasses.py and its "dataclass_*.py" modules into the
new Lib/test/test_dataclasses/ subdirectory.

6 files changed, 4687 insertions, 0 deletions

diff --git a/Lib/test/test_dataclasses/__init__.py b/Lib/test/test_dataclasses/__init__.py
new file mode 100644
index 0000000..7c07dfc
--- /dev/null
+++ b/Lib/test/test_dataclasses/__init__.py
@@ -0,0 +1,4547 @@
+# Deliberately use "from dataclasses import *".  Every name in __all__
+# is tested, so they all must be present.  This is a way to catch
+# missing ones.
+
+from dataclasses import *
+
+import abc
+import io
+import pickle
+import inspect
+import builtins
+import types
+import weakref
+import traceback
+import unittest
+from unittest.mock import Mock
+from typing import ClassVar, Any, List, Union, Tuple, Dict, Generic, TypeVar, Optional, Protocol, DefaultDict
+from typing import get_type_hints
+from collections import deque, OrderedDict, namedtuple, defaultdict
+from functools import total_ordering
+
+import typing       # Needed for the string "typing.ClassVar[int]" to work as an annotation.
+import dataclasses  # Needed for the string "dataclasses.InitVar[int]" to work as an annotation.
+
+# Just any custom exception we can catch.
+class CustomError(Exception): pass
+
+class TestCase(unittest.TestCase):
+    def test_no_fields(self):
+        @dataclass
+        class C:
+            pass
+
+        o = C()
+        self.assertEqual(len(fields(C)), 0)
+
+    def test_no_fields_but_member_variable(self):
+        @dataclass
+        class C:
+            i = 0
+
+        o = C()
+        self.assertEqual(len(fields(C)), 0)
+
+    def test_one_field_no_default(self):
+        @dataclass
+        class C:
+            x: int
+
+        o = C(42)
+        self.assertEqual(o.x, 42)
+
+    def test_field_default_default_factory_error(self):
+        msg = "cannot specify both default and default_factory"
+        with self.assertRaisesRegex(ValueError, msg):
+            @dataclass
+            class C:
+                x: int = field(default=1, default_factory=int)
+
+    def test_field_repr(self):
+        int_field = field(default=1, init=True, repr=False)
+        int_field.name = "id"
+        repr_output = repr(int_field)
+        expected_output = "Field(name='id',type=None," \
+                           f"default=1,default_factory={MISSING!r}," \
+                           "init=True,repr=False,hash=None," \
+                           "compare=True,metadata=mappingproxy({})," \
+                           f"kw_only={MISSING!r}," \
+                           "_field_type=None)"
+
+        self.assertEqual(repr_output, expected_output)
+
+    def test_field_recursive_repr(self):
+        rec_field = field()
+        rec_field.type = rec_field
+        rec_field.name = "id"
+        repr_output = repr(rec_field)
+
+        self.assertIn(",type=...,", repr_output)
+
+    def test_recursive_annotation(self):
+        class C:
+            pass
+
+        @dataclass
+        class D:
+            C: C = field()
+
+        self.assertIn(",type=...,", repr(D.__dataclass_fields__["C"]))
+
+    def test_dataclass_params_repr(self):
+        # Even though this is testing an internal implementation detail,
+        # it's testing a feature we want to make sure is correctly implemented
+        # for the sake of dataclasses itself
+        @dataclass(slots=True, frozen=True)
+        class Some: pass
+
+        repr_output = repr(Some.__dataclass_params__)
+        expected_output = "_DataclassParams(init=True,repr=True," \
+                          "eq=True,order=False,unsafe_hash=False,frozen=True," \
+                          "match_args=True,kw_only=False," \
+                          "slots=True,weakref_slot=False)"
+        self.assertEqual(repr_output, expected_output)
+
+    def test_dataclass_params_signature(self):
+        # Even though this is testing an internal implementation detail,
+        # it's testing a feature we want to make sure is correctly implemented
+        # for the sake of dataclasses itself
+        @dataclass
+        class Some: pass
+
+        for param in inspect.signature(dataclass).parameters:
+            if param == 'cls':
+                continue
+            self.assertTrue(hasattr(Some.__dataclass_params__, param), msg=param)
+
+    def test_named_init_params(self):
+        @dataclass
+        class C:
+            x: int
+
+        o = C(x=32)
+        self.assertEqual(o.x, 32)
+
+    def test_two_fields_one_default(self):
+        @dataclass
+        class C:
+            x: int
+            y: int = 0
+
+        o = C(3)
+        self.assertEqual((o.x, o.y), (3, 0))
+
+        # Non-defaults following defaults.
+        with self.assertRaisesRegex(TypeError,
+                                    "non-default argument 'y' follows "
+                                    "default argument 'x'"):
+            @dataclass
+            class C:
+                x: int = 0
+                y: int
+
+        # A derived class adds a non-default field after a default one.
+        with self.assertRaisesRegex(TypeError,
+                                    "non-default argument 'y' follows "
+                                    "default argument 'x'"):
+            @dataclass
+            class B:
+                x: int = 0
+
+            @dataclass
+            class C(B):
+                y: int
+
+        # Override a base class field and add a default to
+        #  a field which didn't use to have a default.
+        with self.assertRaisesRegex(TypeError,
+                                    "non-default argument 'y' follows "
+                                    "default argument 'x'"):
+            @dataclass
+            class B:
+                x: int
+                y: int
+
+            @dataclass
+            class C(B):
+                x: int = 0
+
+    def test_overwrite_hash(self):
+        # Test that declaring this class isn't an error.  It should
+        #  use the user-provided __hash__.
+        @dataclass(frozen=True)
+        class C:
+            x: int
+            def __hash__(self):
+                return 301
+        self.assertEqual(hash(C(100)), 301)
+
+        # Test that declaring this class isn't an error.  It should
+        #  use the generated __hash__.
+        @dataclass(frozen=True)
+        class C:
+            x: int
+            def __eq__(self, other):
+                return False
+        self.assertEqual(hash(C(100)), hash((100,)))
+
+        # But this one should generate an exception, because with
+        #  unsafe_hash=True, it's an error to have a __hash__ defined.
+        with self.assertRaisesRegex(TypeError,
+                                    'Cannot overwrite attribute __hash__'):
+            @dataclass(unsafe_hash=True)
+            class C:
+                def __hash__(self):
+                    pass
+
+        # Creating this class should not generate an exception,
+        #  because even though __hash__ exists before @dataclass is
+        #  called, (due to __eq__ being defined), since it's None
+        #  that's okay.
+        @dataclass(unsafe_hash=True)
+        class C:
+            x: int
+            def __eq__(self):
+                pass
+        # The generated hash function works as we'd expect.
+        self.assertEqual(hash(C(10)), hash((10,)))
+
+        # Creating this class should generate an exception, because
+        #  __hash__ exists and is not None, which it would be if it
+        #  had been auto-generated due to __eq__ being defined.
+        with self.assertRaisesRegex(TypeError,
+                                    'Cannot overwrite attribute __hash__'):
+            @dataclass(unsafe_hash=True)
+            class C:
+                x: int
+                def __eq__(self):
+                    pass
+                def __hash__(self):
+                    pass
+
+    def test_overwrite_fields_in_derived_class(self):
+        # Note that x from C1 replaces x in Base, but the order remains
+        #  the same as defined in Base.
+        @dataclass
+        class Base:
+            x: Any = 15.0
+            y: int = 0
+
+        @dataclass
+        class C1(Base):
+            z: int = 10
+            x: int = 15
+
+        o = Base()
+        self.assertEqual(repr(o), 'TestCase.test_overwrite_fields_in_derived_class.<locals>.Base(x=15.0, y=0)')
+
+        o = C1()
+        self.assertEqual(repr(o), 'TestCase.test_overwrite_fields_in_derived_class.<locals>.C1(x=15, y=0, z=10)')
+
+        o = C1(x=5)
+        self.assertEqual(repr(o), 'TestCase.test_overwrite_fields_in_derived_class.<locals>.C1(x=5, y=0, z=10)')
+
+    def test_field_named_self(self):
+        @dataclass
+        class C:
+            self: str
+        c=C('foo')
+        self.assertEqual(c.self, 'foo')
+
+        # Make sure the first parameter is not named 'self'.
+        sig = inspect.signature(C.__init__)
+        first = next(iter(sig.parameters))
+        self.assertNotEqual('self', first)
+
+        # But we do use 'self' if no field named self.
+        @dataclass
+        class C:
+            selfx: str
+
+        # Make sure the first parameter is named 'self'.
+        sig = inspect.signature(C.__init__)
+        first = next(iter(sig.parameters))
+        self.assertEqual('self', first)
+
+    def test_field_named_object(self):
+        @dataclass
+        class C:
+            object: str
+        c = C('foo')
+        self.assertEqual(c.object, 'foo')
+
+    def test_field_named_object_frozen(self):
+        @dataclass(frozen=True)
+        class C:
+            object: str
+        c = C('foo')
+        self.assertEqual(c.object, 'foo')
+
+    def test_field_named_BUILTINS_frozen(self):
+        # gh-96151
+        @dataclass(frozen=True)
+        class C:
+            BUILTINS: int
+        c = C(5)
+        self.assertEqual(c.BUILTINS, 5)
+
+    def test_field_with_special_single_underscore_names(self):
+        # gh-98886
+
+        @dataclass
+        class X:
+            x: int = field(default_factory=lambda: 111)
+            _dflt_x: int = field(default_factory=lambda: 222)
+
+        X()
+
+        @dataclass
+        class Y:
+            y: int = field(default_factory=lambda: 111)
+            _HAS_DEFAULT_FACTORY: int = 222
+
+        assert Y(y=222).y == 222
+
+    def test_field_named_like_builtin(self):
+        # Attribute names can shadow built-in names
+        # since code generation is used.
+        # Ensure that this is not happening.
+        exclusions = {'None', 'True', 'False'}
+        builtins_names = sorted(
+            b for b in builtins.__dict__.keys()
+            if not b.startswith('__') and b not in exclusions
+        )
+        attributes = [(name, str) for name in builtins_names]
+        C = make_dataclass('C', attributes)
+
+        c = C(*[name for name in builtins_names])
+
+        for name in builtins_names:
+            self.assertEqual(getattr(c, name), name)
+
+    def test_field_named_like_builtin_frozen(self):
+        # Attribute names can shadow built-in names
+        # since code generation is used.
+        # Ensure that this is not happening
+        # for frozen data classes.
+        exclusions = {'None', 'True', 'False'}
+        builtins_names = sorted(
+            b for b in builtins.__dict__.keys()
+            if not b.startswith('__') and b not in exclusions
+        )
+        attributes = [(name, str) for name in builtins_names]
+        C = make_dataclass('C', attributes, frozen=True)
+
+        c = C(*[name for name in builtins_names])
+
+        for name in builtins_names:
+            self.assertEqual(getattr(c, name), name)
+
+    def test_0_field_compare(self):
+        # Ensure that order=False is the default.
+        @dataclass
+        class C0:
+            pass
+
+        @dataclass(order=False)
+        class C1:
+            pass
+
+        for cls in [C0, C1]:
+            with self.subTest(cls=cls):
+                self.assertEqual(cls(), cls())
+                for idx, fn in enumerate([lambda a, b: a < b,
+                                          lambda a, b: a <= b,
+                                          lambda a, b: a > b,
+                                          lambda a, b: a >= b]):
+                    with self.subTest(idx=idx):
+                        with self.assertRaisesRegex(TypeError,
+                                                    f"not supported between instances of '{cls.__name__}' and '{cls.__name__}'"):
+                            fn(cls(), cls())
+
+        @dataclass(order=True)
+        class C:
+            pass
+        self.assertLessEqual(C(), C())
+        self.assertGreaterEqual(C(), C())
+
+    def test_1_field_compare(self):
+        # Ensure that order=False is the default.
+        @dataclass
+        class C0:
+            x: int
+
+        @dataclass(order=False)
+        class C1:
+            x: int
+
+        for cls in [C0, C1]:
+            with self.subTest(cls=cls):
+                self.assertEqual(cls(1), cls(1))
+                self.assertNotEqual(cls(0), cls(1))
+                for idx, fn in enumerate([lambda a, b: a < b,
+                                          lambda a, b: a <= b,
+                                          lambda a, b: a > b,
+                                          lambda a, b: a >= b]):
+                    with self.subTest(idx=idx):
+                        with self.assertRaisesRegex(TypeError,
+                                                    f"not supported between instances of '{cls.__name__}' and '{cls.__name__}'"):
+                            fn(cls(0), cls(0))
+
+        @dataclass(order=True)
+        class C:
+            x: int
+        self.assertLess(C(0), C(1))
+        self.assertLessEqual(C(0), C(1))
+        self.assertLessEqual(C(1), C(1))
+        self.assertGreater(C(1), C(0))
+        self.assertGreaterEqual(C(1), C(0))
+        self.assertGreaterEqual(C(1), C(1))
+
+    def test_simple_compare(self):
+        # Ensure that order=False is the default.
+        @dataclass
+        class C0:
+            x: int
+            y: int
+
+        @dataclass(order=False)
+        class C1:
+            x: int
+            y: int
+
+        for cls in [C0, C1]:
+            with self.subTest(cls=cls):
+                self.assertEqual(cls(0, 0), cls(0, 0))
+                self.assertEqual(cls(1, 2), cls(1, 2))
+                self.assertNotEqual(cls(1, 0), cls(0, 0))
+                self.assertNotEqual(cls(1, 0), cls(1, 1))
+                for idx, fn in enumerate([lambda a, b: a < b,
+                                          lambda a, b: a <= b,
+                                          lambda a, b: a > b,
+                                          lambda a, b: a >= b]):
+                    with self.subTest(idx=idx):
+                        with self.assertRaisesRegex(TypeError,
+                                                    f"not supported between instances of '{cls.__name__}' and '{cls.__name__}'"):
+                            fn(cls(0, 0), cls(0, 0))
+
+        @dataclass(order=True)
+        class C:
+            x: int
+            y: int
+
+        for idx, fn in enumerate([lambda a, b: a == b,
+                                  lambda a, b: a <= b,
+                                  lambda a, b: a >= b]):
+            with self.subTest(idx=idx):
+                self.assertTrue(fn(C(0, 0), C(0, 0)))
+
+        for idx, fn in enumerate([lambda a, b: a < b,
+                                  lambda a, b: a <= b,
+                                  lambda a, b: a != b]):
+            with self.subTest(idx=idx):
+                self.assertTrue(fn(C(0, 0), C(0, 1)))
+                self.assertTrue(fn(C(0, 1), C(1, 0)))
+                self.assertTrue(fn(C(1, 0), C(1, 1)))
+
+        for idx, fn in enumerate([lambda a, b: a > b,
+                                  lambda a, b: a >= b,
+                                  lambda a, b: a != b]):
+            with self.subTest(idx=idx):
+                self.assertTrue(fn(C(0, 1), C(0, 0)))
+                self.assertTrue(fn(C(1, 0), C(0, 1)))
+                self.assertTrue(fn(C(1, 1), C(1, 0)))
+
+    def test_compare_subclasses(self):
+        # Comparisons fail for subclasses, even if no fields
+        #  are added.
+        @dataclass
+        class B:
+            i: int
+
+        @dataclass
+        class C(B):
+            pass
+
+        for idx, (fn, expected) in enumerate([(lambda a, b: a == b, False),
+                                              (lambda a, b: a != b, True)]):
+            with self.subTest(idx=idx):
+                self.assertEqual(fn(B(0), C(0)), expected)
+
+        for idx, fn in enumerate([lambda a, b: a < b,
+                                  lambda a, b: a <= b,
+                                  lambda a, b: a > b,
+                                  lambda a, b: a >= b]):
+            with self.subTest(idx=idx):
+                with self.assertRaisesRegex(TypeError,
+                                            "not supported between instances of 'B' and 'C'"):
+                    fn(B(0), C(0))
+
+    def test_eq_order(self):
+        # Test combining eq and order.
+        for (eq,    order, result   ) in [
+            (False, False, 'neither'),
+            (False, True,  'exception'),
+            (True,  False, 'eq_only'),
+            (True,  True,  'both'),
+        ]:
+            with self.subTest(eq=eq, order=order):
+                if result == 'exception':
+                    with self.assertRaisesRegex(ValueError, 'eq must be true if order is true'):
+                        @dataclass(eq=eq, order=order)
+                        class C:
+                            pass
+                else:
+                    @dataclass(eq=eq, order=order)
+                    class C:
+                        pass
+
+                    if result == 'neither':
+                        self.assertNotIn('__eq__', C.__dict__)
+                        self.assertNotIn('__lt__', C.__dict__)
+                        self.assertNotIn('__le__', C.__dict__)
+                        self.assertNotIn('__gt__', C.__dict__)
+                        self.assertNotIn('__ge__', C.__dict__)
+                    elif result == 'both':
+                        self.assertIn('__eq__', C.__dict__)
+                        self.assertIn('__lt__', C.__dict__)
+                        self.assertIn('__le__', C.__dict__)
+                        self.assertIn('__gt__', C.__dict__)
+                        self.assertIn('__ge__', C.__dict__)
+                    elif result == 'eq_only':
+                        self.assertIn('__eq__', C.__dict__)
+                        self.assertNotIn('__lt__', C.__dict__)
+                        self.assertNotIn('__le__', C.__dict__)
+                        self.assertNotIn('__gt__', C.__dict__)
+                        self.assertNotIn('__ge__', C.__dict__)
+                    else:
+                        assert False, f'unknown result {result!r}'
+
+    def test_field_no_default(self):
+        @dataclass
+        class C:
+            x: int = field()
+
+        self.assertEqual(C(5).x, 5)
+
+        with self.assertRaisesRegex(TypeError,
+                                    r"__init__\(\) missing 1 required "
+                                    "positional argument: 'x'"):
+            C()
+
+    def test_field_default(self):
+        default = object()
+        @dataclass
+        class C:
+            x: object = field(default=default)
+
+        self.assertIs(C.x, default)
+        c = C(10)
+        self.assertEqual(c.x, 10)
+
+        # If we delete the instance attribute, we should then see the
+        #  class attribute.
+        del c.x
+        self.assertIs(c.x, default)
+
+        self.assertIs(C().x, default)
+
+    def test_not_in_repr(self):
+        @dataclass
+        class C:
+            x: int = field(repr=False)
+        with self.assertRaises(TypeError):
+            C()
+        c = C(10)
+        self.assertEqual(repr(c), 'TestCase.test_not_in_repr.<locals>.C()')
+
+        @dataclass
+        class C:
+            x: int = field(repr=False)
+            y: int
+        c = C(10, 20)
+        self.assertEqual(repr(c), 'TestCase.test_not_in_repr.<locals>.C(y=20)')
+
+    def test_not_in_compare(self):
+        @dataclass
+        class C:
+            x: int = 0
+            y: int = field(compare=False, default=4)
+
+        self.assertEqual(C(), C(0, 20))
+        self.assertEqual(C(1, 10), C(1, 20))
+        self.assertNotEqual(C(3), C(4, 10))
+        self.assertNotEqual(C(3, 10), C(4, 10))
+
+    def test_no_unhashable_default(self):
+        # See bpo-44674.
+        class Unhashable:
+            __hash__ = None
+
+        unhashable_re = 'mutable default .* for field a is not allowed'
+        with self.assertRaisesRegex(ValueError, unhashable_re):
+            @dataclass
+            class A:
+                a: dict = {}
+
+        with self.assertRaisesRegex(ValueError, unhashable_re):
+            @dataclass
+            class A:
+                a: Any = Unhashable()
+
+        # Make sure that the machinery looking for hashability is using the
+        # class's __hash__, not the instance's __hash__.
+        with self.assertRaisesRegex(ValueError, unhashable_re):
+            unhashable = Unhashable()
+            # This shouldn't make the variable hashable.
+            unhashable.__hash__ = lambda: 0
+            @dataclass
+            class A:
+                a: Any = unhashable
+
+    def test_hash_field_rules(self):
+        # Test all 6 cases of:
+        #  hash=True/False/None
+        #  compare=True/False
+        for (hash_,    compare, result  ) in [
+            (True,     False,   'field' ),
+            (True,     True,    'field' ),
+            (False,    False,   'absent'),
+            (False,    True,    'absent'),
+            (None,     False,   'absent'),
+            (None,     True,    'field' ),
+            ]:
+            with self.subTest(hash=hash_, compare=compare):
+                @dataclass(unsafe_hash=True)
+                class C:
+                    x: int = field(compare=compare, hash=hash_, default=5)
+
+                if result == 'field':
+                    # __hash__ contains the field.
+                    self.assertEqual(hash(C(5)), hash((5,)))
+                elif result == 'absent':
+                    # The field is not present in the hash.
+                    self.assertEqual(hash(C(5)), hash(()))
+                else:
+                    assert False, f'unknown result {result!r}'
+
+    def test_init_false_no_default(self):
+        # If init=False and no default value, then the field won't be
+        #  present in the instance.
+        @dataclass
+        class C:
+            x: int = field(init=False)
+
+        self.assertNotIn('x', C().__dict__)
+
+        @dataclass
+        class C:
+            x: int
+            y: int = 0
+            z: int = field(init=False)
+            t: int = 10
+
+        self.assertNotIn('z', C(0).__dict__)
+        self.assertEqual(vars(C(5)), {'t': 10, 'x': 5, 'y': 0})
+
+    def test_class_marker(self):
+        @dataclass
+        class C:
+            x: int
+            y: str = field(init=False, default=None)
+            z: str = field(repr=False)
+
+        the_fields = fields(C)
+        # the_fields is a tuple of 3 items, each value
+        #  is in __annotations__.
+        self.assertIsInstance(the_fields, tuple)
+        for f in the_fields:
+            self.assertIs(type(f), Field)
+            self.assertIn(f.name, C.__annotations__)
+
+        self.assertEqual(len(the_fields), 3)
+
+        self.assertEqual(the_fields[0].name, 'x')
+        self.assertEqual(the_fields[0].type, int)
+        self.assertFalse(hasattr(C, 'x'))
+        self.assertTrue (the_fields[0].init)
+        self.assertTrue (the_fields[0].repr)
+        self.assertEqual(the_fields[1].name, 'y')
+        self.assertEqual(the_fields[1].type, str)
+        self.assertIsNone(getattr(C, 'y'))
+        self.assertFalse(the_fields[1].init)
+        self.assertTrue (the_fields[1].repr)
+        self.assertEqual(the_fields[2].name, 'z')
+        self.assertEqual(the_fields[2].type, str)
+        self.assertFalse(hasattr(C, 'z'))
+        self.assertTrue (the_fields[2].init)
+        self.assertFalse(the_fields[2].repr)
+
+    def test_field_order(self):
+        @dataclass
+        class B:
+            a: str = 'B:a'
+            b: str = 'B:b'
+            c: str = 'B:c'
+
+        @dataclass
+        class C(B):
+            b: str = 'C:b'
+
+        self.assertEqual([(f.name, f.default) for f in fields(C)],
+                         [('a', 'B:a'),
+                          ('b', 'C:b'),
+                          ('c', 'B:c')])
+
+        @dataclass
+        class D(B):
+            c: str = 'D:c'
+
+        self.assertEqual([(f.name, f.default) for f in fields(D)],
+                         [('a', 'B:a'),
+                          ('b', 'B:b'),
+                          ('c', 'D:c')])
+
+        @dataclass
+        class E(D):
+            a: str = 'E:a'
+            d: str = 'E:d'
+
+        self.assertEqual([(f.name, f.default) for f in fields(E)],
+                         [('a', 'E:a'),
+                          ('b', 'B:b'),
+                          ('c', 'D:c'),
+                          ('d', 'E:d')])
+
+    def test_class_attrs(self):
+        # We only have a class attribute if a default value is
+        #  specified, either directly or via a field with a default.
+        default = object()
+        @dataclass
+        class C:
+            x: int
+            y: int = field(repr=False)
+            z: object = default
+            t: int = field(default=100)
+
+        self.assertFalse(hasattr(C, 'x'))
+        self.assertFalse(hasattr(C, 'y'))
+        self.assertIs   (C.z, default)
+        self.assertEqual(C.t, 100)
+
+    def test_disallowed_mutable_defaults(self):
+        # For the known types, don't allow mutable default values.
+        for typ, empty, non_empty in [(list, [], [1]),
+                                      (dict, {}, {0:1}),
+                                      (set, set(), set([1])),
+                                      ]:
+            with self.subTest(typ=typ):
+                # Can't use a zero-length value.
+                with self.assertRaisesRegex(ValueError,
+                                            f'mutable default {typ} for field '
+                                            'x is not allowed'):
+                    @dataclass
+                    class Point:
+                        x: typ = empty
+
+
+                # Nor a non-zero-length value
+                with self.assertRaisesRegex(ValueError,
+                                            f'mutable default {typ} for field '
+                                            'y is not allowed'):
+                    @dataclass
+                    class Point:
+                        y: typ = non_empty
+
+                # Check subtypes also fail.
+                class Subclass(typ): pass
+
+                with self.assertRaisesRegex(ValueError,
+                                            "mutable default .*Subclass'>"
+                                            " for field z is not allowed"
+                                            ):
+                    @dataclass
+                    class Point:
+                        z: typ = Subclass()
+
+                # Because this is a ClassVar, it can be mutable.
+                @dataclass
+                class C:
+                    z: ClassVar[typ] = typ()
+
+                # Because this is a ClassVar, it can be mutable.
+                @dataclass
+                class C:
+                    x: ClassVar[typ] = Subclass()
+
+    def test_deliberately_mutable_defaults(self):
+        # If a mutable default isn't in the known list of
+        #  (list, dict, set), then it's okay.
+        class Mutable:
+            def __init__(self):
+                self.l = []
+
+        @dataclass
+        class C:
+            x: Mutable
+
+        # These 2 instances will share this value of x.
+        lst = Mutable()
+        o1 = C(lst)
+        o2 = C(lst)
+        self.assertEqual(o1, o2)
+        o1.x.l.extend([1, 2])
+        self.assertEqual(o1, o2)
+        self.assertEqual(o1.x.l, [1, 2])
+        self.assertIs(o1.x, o2.x)
+
+    def test_no_options(self):
+        # Call with dataclass().
+        @dataclass()
+        class C:
+            x: int
+
+        self.assertEqual(C(42).x, 42)
+
+    def test_not_tuple(self):
+        # Make sure we can't be compared to a tuple.
+        @dataclass
+        class Point:
+            x: int
+            y: int
+        self.assertNotEqual(Point(1, 2), (1, 2))
+
+        # And that we can't compare to another unrelated dataclass.
+        @dataclass
+        class C:
+            x: int
+            y: int
+        self.assertNotEqual(Point(1, 3), C(1, 3))
+
+    def test_not_other_dataclass(self):
+        # Test that some of the problems with namedtuple don't happen
+        #  here.
+        @dataclass
+        class Point3D:
+            x: int
+            y: int
+            z: int
+
+        @dataclass
+        class Date:
+            year: int
+            month: int
+            day: int
+
+        self.assertNotEqual(Point3D(2017, 6, 3), Date(2017, 6, 3))
+        self.assertNotEqual(Point3D(1, 2, 3), (1, 2, 3))
+
+        # Make sure we can't unpack.
+        with self.assertRaisesRegex(TypeError, 'unpack'):
+            x, y, z = Point3D(4, 5, 6)
+
+        # Make sure another class with the same field names isn't
+        #  equal.
+        @dataclass
+        class Point3Dv1:
+            x: int = 0
+            y: int = 0
+            z: int = 0
+        self.assertNotEqual(Point3D(0, 0, 0), Point3Dv1())
+
+    def test_function_annotations(self):
+        # Some dummy class and instance to use as a default.
+        class F:
+            pass
+        f = F()
+
+        def validate_class(cls):
+            # First, check __annotations__, even though they're not
+            #  function annotations.
+            self.assertEqual(cls.__annotations__['i'], int)
+            self.assertEqual(cls.__annotations__['j'], str)
+            self.assertEqual(cls.__annotations__['k'], F)
+            self.assertEqual(cls.__annotations__['l'], float)
+            self.assertEqual(cls.__annotations__['z'], complex)
+
+            # Verify __init__.
+
+            signature = inspect.signature(cls.__init__)
+            # Check the return type, should be None.
+            self.assertIs(signature.return_annotation, None)
+
+            # Check each parameter.
+            params = iter(signature.parameters.values())
+            param = next(params)
+            # This is testing an internal name, and probably shouldn't be tested.
+            self.assertEqual(param.name, 'self')
+            param = next(params)
+            self.assertEqual(param.name, 'i')
+            self.assertIs   (param.annotation, int)
+            self.assertEqual(param.default, inspect.Parameter.empty)
+            self.assertEqual(param.kind, inspect.Parameter.POSITIONAL_OR_KEYWORD)
+            param = next(params)
+            self.assertEqual(param.name, 'j')
+            self.assertIs   (param.annotation, str)
+            self.assertEqual(param.default, inspect.Parameter.empty)
+            self.assertEqual(param.kind, inspect.Parameter.POSITIONAL_OR_KEYWORD)
+            param = next(params)
+            self.assertEqual(param.name, 'k')
+            self.assertIs   (param.annotation, F)
+            # Don't test for the default, since it's set to MISSING.
+            self.assertEqual(param.kind, inspect.Parameter.POSITIONAL_OR_KEYWORD)
+            param = next(params)
+            self.assertEqual(param.name, 'l')
+            self.assertIs   (param.annotation, float)
+            # Don't test for the default, since it's set to MISSING.
+            self.assertEqual(param.kind, inspect.Parameter.POSITIONAL_OR_KEYWORD)
+            self.assertRaises(StopIteration, next, params)
+
+
+        @dataclass
+        class C:
+            i: int
+            j: str
+            k: F = f
+            l: float=field(default=None)
+            z: complex=field(default=3+4j, init=False)
+
+        validate_class(C)
+
+        # Now repeat with __hash__.
+        @dataclass(frozen=True, unsafe_hash=True)
+        class C:
+            i: int
+            j: str
+            k: F = f
+            l: float=field(default=None)
+            z: complex=field(default=3+4j, init=False)
+
+        validate_class(C)
+
+    def test_missing_default(self):
+        # Test that MISSING works the same as a default not being
+        #  specified.
+        @dataclass
+        class C:
+            x: int=field(default=MISSING)
+        with self.assertRaisesRegex(TypeError,
+                                    r'__init__\(\) missing 1 required '
+                                    'positional argument'):
+            C()
+        self.assertNotIn('x', C.__dict__)
+
+        @dataclass
+        class D:
+            x: int
+        with self.assertRaisesRegex(TypeError,
+                                    r'__init__\(\) missing 1 required '
+                                    'positional argument'):
+            D()
+        self.assertNotIn('x', D.__dict__)
+
+    def test_missing_default_factory(self):
+        # Test that MISSING works the same as a default factory not
+        #  being specified (which is really the same as a default not
+        #  being specified, too).
+        @dataclass
+        class C:
+            x: int=field(default_factory=MISSING)
+        with self.assertRaisesRegex(TypeError,
+                                    r'__init__\(\) missing 1 required '
+                                    'positional argument'):
+            C()
+        self.assertNotIn('x', C.__dict__)
+
+        @dataclass
+        class D:
+            x: int=field(default=MISSING, default_factory=MISSING)
+        with self.assertRaisesRegex(TypeError,
+                                    r'__init__\(\) missing 1 required '
+                                    'positional argument'):
+            D()
+        self.assertNotIn('x', D.__dict__)
+
+    def test_missing_repr(self):
+        self.assertIn('MISSING_TYPE object', repr(MISSING))
+
+    def test_dont_include_other_annotations(self):
+        @dataclass
+        class C:
+            i: int
+            def foo(self) -> int:
+                return 4
+            @property
+            def bar(self) -> int:
+                return 5
+        self.assertEqual(list(C.__annotations__), ['i'])
+        self.assertEqual(C(10).foo(), 4)
+        self.assertEqual(C(10).bar, 5)
+        self.assertEqual(C(10).i, 10)
+
+    def test_post_init(self):
+        # Just make sure it gets called
+        @dataclass
+        class C:
+            def __post_init__(self):
+                raise CustomError()
+        with self.assertRaises(CustomError):
+            C()
+
+        @dataclass
+        class C:
+            i: int = 10
+            def __post_init__(self):
+                if self.i == 10:
+                    raise CustomError()
+        with self.assertRaises(CustomError):
+            C()
+        # post-init gets called, but doesn't raise. This is just
+        #  checking that self is used correctly.
+        C(5)
+
+        # If there's not an __init__, then post-init won't get called.
+        @dataclass(init=False)
+        class C:
+            def __post_init__(self):
+                raise CustomError()
+        # Creating the class won't raise
+        C()
+
+        @dataclass
+        class C:
+            x: int = 0
+            def __post_init__(self):
+                self.x *= 2
+        self.assertEqual(C().x, 0)
+        self.assertEqual(C(2).x, 4)
+
+        # Make sure that if we're frozen, post-init can't set
+        #  attributes.
+        @dataclass(frozen=True)
+        class C:
+            x: int = 0
+            def __post_init__(self):
+                self.x *= 2
+        with self.assertRaises(FrozenInstanceError):
+            C()
+
+    def test_post_init_super(self):
+        # Make sure super() post-init isn't called by default.
+        class B:
+            def __post_init__(self):
+                raise CustomError()
+
+        @dataclass
+        class C(B):
+            def __post_init__(self):
+                self.x = 5
+
+        self.assertEqual(C().x, 5)
+
+        # Now call super(), and it will raise.
+        @dataclass
+        class C(B):
+            def __post_init__(self):
+                super().__post_init__()
+
+        with self.assertRaises(CustomError):
+            C()
+
+        # Make sure post-init is called, even if not defined in our
+        #  class.
+        @dataclass
+        class C(B):
+            pass
+
+        with self.assertRaises(CustomError):
+            C()
+
+    def test_post_init_staticmethod(self):
+        flag = False
+        @dataclass
+        class C:
+            x: int
+            y: int
+            @staticmethod
+            def __post_init__():
+                nonlocal flag
+                flag = True
+
+        self.assertFalse(flag)
+        c = C(3, 4)
+        self.assertEqual((c.x, c.y), (3, 4))
+        self.assertTrue(flag)
+
+    def test_post_init_classmethod(self):
+        @dataclass
+        class C:
+            flag = False
+            x: int
+            y: int
+            @classmethod
+            def __post_init__(cls):
+                cls.flag = True
+
+        self.assertFalse(C.flag)
+        c = C(3, 4)
+        self.assertEqual((c.x, c.y), (3, 4))
+        self.assertTrue(C.flag)
+
+    def test_post_init_not_auto_added(self):
+        # See bpo-46757, which had proposed always adding __post_init__.  As
+        # Raymond Hettinger pointed out, that would be a breaking change.  So,
+        # add a test to make sure that the current behavior doesn't change.
+
+        @dataclass
+        class A0:
+            pass
+
+        @dataclass
+        class B0:
+            b_called: bool = False
+            def __post_init__(self):
+                self.b_called = True
+
+        @dataclass
+        class C0(A0, B0):
+            c_called: bool = False
+            def __post_init__(self):
+                super().__post_init__()
+                self.c_called = True
+
+        # Since A0 has no __post_init__, and one wasn't automatically added
+        # (because that's the rule: it's never added by @dataclass, it's only
+        # the class author that can add it), then B0.__post_init__ is called.
+        # Verify that.
+        c = C0()
+        self.assertTrue(c.b_called)
+        self.assertTrue(c.c_called)
+
+        ######################################
+        # Now, the same thing, except A1 defines __post_init__.
+        @dataclass
+        class A1:
+            def __post_init__(self):
+                pass
+
+        @dataclass
+        class B1:
+            b_called: bool = False
+            def __post_init__(self):
+                self.b_called = True
+
+        @dataclass
+        class C1(A1, B1):
+            c_called: bool = False
+            def __post_init__(self):
+                super().__post_init__()
+                self.c_called = True
+
+        # This time, B1.__post_init__ isn't being called.  This mimics what
+        # would happen if A1.__post_init__ had been automatically added,
+        # instead of manually added as we see here.  This test isn't really
+        # needed, but I'm including it just to demonstrate the changed
+        # behavior when A1 does define __post_init__.
+        c = C1()
+        self.assertFalse(c.b_called)
+        self.assertTrue(c.c_called)
+
+    def test_class_var(self):
+        # Make sure ClassVars are ignored in __init__, __repr__, etc.
+        @dataclass
+        class C:
+            x: int
+            y: int = 10
+            z: ClassVar[int] = 1000
+            w: ClassVar[int] = 2000
+            t: ClassVar[int] = 3000
+            s: ClassVar      = 4000
+
+        c = C(5)
+        self.assertEqual(repr(c), 'TestCase.test_class_var.<locals>.C(x=5, y=10)')
+        self.assertEqual(len(fields(C)), 2)                 # We have 2 fields.
+        self.assertEqual(len(C.__annotations__), 6)         # And 4 ClassVars.
+        self.assertEqual(c.z, 1000)
+        self.assertEqual(c.w, 2000)
+        self.assertEqual(c.t, 3000)
+        self.assertEqual(c.s, 4000)
+        C.z += 1
+        self.assertEqual(c.z, 1001)
+        c = C(20)
+        self.assertEqual((c.x, c.y), (20, 10))
+        self.assertEqual(c.z, 1001)
+        self.assertEqual(c.w, 2000)
+        self.assertEqual(c.t, 3000)
+        self.assertEqual(c.s, 4000)
+
+    def test_class_var_no_default(self):
+        # If a ClassVar has no default value, it should not be set on the class.
+        @dataclass
+        class C:
+            x: ClassVar[int]
+
+        self.assertNotIn('x', C.__dict__)
+
+    def test_class_var_default_factory(self):
+        # It makes no sense for a ClassVar to have a default factory. When
+        #  would it be called? Call it yourself, since it's class-wide.
+        with self.assertRaisesRegex(TypeError,
+                                    'cannot have a default factory'):
+            @dataclass
+            class C:
+                x: ClassVar[int] = field(default_factory=int)
+
+            self.assertNotIn('x', C.__dict__)
+
+    def test_class_var_with_default(self):
+        # If a ClassVar has a default value, it should be set on the class.
+        @dataclass
+        class C:
+            x: ClassVar[int] = 10
+        self.assertEqual(C.x, 10)
+
+        @dataclass
+        class C:
+            x: ClassVar[int] = field(default=10)
+        self.assertEqual(C.x, 10)
+
+    def test_class_var_frozen(self):
+        # Make sure ClassVars work even if we're frozen.
+        @dataclass(frozen=True)
+        class C:
+            x: int
+            y: int = 10
+            z: ClassVar[int] = 1000
+            w: ClassVar[int] = 2000
+            t: ClassVar[int] = 3000
+
+        c = C(5)
+        self.assertEqual(repr(C(5)), 'TestCase.test_class_var_frozen.<locals>.C(x=5, y=10)')
+        self.assertEqual(len(fields(C)), 2)                 # We have 2 fields
+        self.assertEqual(len(C.__annotations__), 5)         # And 3 ClassVars
+        self.assertEqual(c.z, 1000)
+        self.assertEqual(c.w, 2000)
+        self.assertEqual(c.t, 3000)
+        # We can still modify the ClassVar, it's only instances that are
+        #  frozen.
+        C.z += 1
+        self.assertEqual(c.z, 1001)
+        c = C(20)
+        self.assertEqual((c.x, c.y), (20, 10))
+        self.assertEqual(c.z, 1001)
+        self.assertEqual(c.w, 2000)
+        self.assertEqual(c.t, 3000)
+
+    def test_init_var_no_default(self):
+        # If an InitVar has no default value, it should not be set on the class.
+        @dataclass
+        class C:
+            x: InitVar[int]
+
+        self.assertNotIn('x', C.__dict__)
+
+    def test_init_var_default_factory(self):
+        # It makes no sense for an InitVar to have a default factory. When
+        #  would it be called? Call it yourself, since it's class-wide.
+        with self.assertRaisesRegex(TypeError,
+                                    'cannot have a default factory'):
+            @dataclass
+            class C:
+                x: InitVar[int] = field(default_factory=int)
+
+            self.assertNotIn('x', C.__dict__)
+
+    def test_init_var_with_default(self):
+        # If an InitVar has a default value, it should be set on the class.
+        @dataclass
+        class C:
+            x: InitVar[int] = 10
+        self.assertEqual(C.x, 10)
+
+        @dataclass
+        class C:
+            x: InitVar[int] = field(default=10)
+        self.assertEqual(C.x, 10)
+
+    def test_init_var(self):
+        @dataclass
+        class C:
+            x: int = None
+            init_param: InitVar[int] = None
+
+            def __post_init__(self, init_param):
+                if self.x is None:
+                    self.x = init_param*2
+
+        c = C(init_param=10)
+        self.assertEqual(c.x, 20)
+
+    def test_init_var_preserve_type(self):
+        self.assertEqual(InitVar[int].type, int)
+
+        # Make sure the repr is correct.
+        self.assertEqual(repr(InitVar[int]), 'dataclasses.InitVar[int]')
+        self.assertEqual(repr(InitVar[List[int]]),
+                         'dataclasses.InitVar[typing.List[int]]')
+        self.assertEqual(repr(InitVar[list[int]]),
+                         'dataclasses.InitVar[list[int]]')
+        self.assertEqual(repr(InitVar[int|str]),
+                         'dataclasses.InitVar[int | str]')
+
+    def test_init_var_inheritance(self):
+        # Note that this deliberately tests that a dataclass need not
+        #  have a __post_init__ function if it has an InitVar field.
+        #  It could just be used in a derived class, as shown here.
+        @dataclass
+        class Base:
+            x: int
+            init_base: InitVar[int]
+
+        # We can instantiate by passing the InitVar, even though
+        #  it's not used.
+        b = Base(0, 10)
+        self.assertEqual(vars(b), {'x': 0})
+
+        @dataclass
+        class C(Base):
+            y: int
+            init_derived: InitVar[int]
+
+            def __post_init__(self, init_base, init_derived):
+                self.x = self.x + init_base
+                self.y = self.y + init_derived
+
+        c = C(10, 11, 50, 51)
+        self.assertEqual(vars(c), {'x': 21, 'y': 101})
+
+    def test_default_factory(self):
+        # Test a factory that returns a new list.
+        @dataclass
+        class C:
+            x: int
+            y: list = field(default_factory=list)
+
+        c0 = C(3)
+        c1 = C(3)
+        self.assertEqual(c0.x, 3)
+        self.assertEqual(c0.y, [])
+        self.assertEqual(c0, c1)
+        self.assertIsNot(c0.y, c1.y)
+        self.assertEqual(astuple(C(5, [1])), (5, [1]))
+
+        # Test a factory that returns a shared list.
+        l = []
+        @dataclass
+        class C:
+            x: int
+            y: list = field(default_factory=lambda: l)
+
+        c0 = C(3)
+        c1 = C(3)
+        self.assertEqual(c0.x, 3)
+        self.assertEqual(c0.y, [])
+        self.assertEqual(c0, c1)
+        self.assertIs(c0.y, c1.y)
+        self.assertEqual(astuple(C(5, [1])), (5, [1]))
+
+        # Test various other field flags.
+        # repr
+        @dataclass
+        class C:
+            x: list = field(default_factory=list, repr=False)
+        self.assertEqual(repr(C()), 'TestCase.test_default_factory.<locals>.C()')
+        self.assertEqual(C().x, [])
+
+        # hash
+        @dataclass(unsafe_hash=True)
+        class C:
+            x: list = field(default_factory=list, hash=False)
+        self.assertEqual(astuple(C()), ([],))
+        self.assertEqual(hash(C()), hash(()))
+
+        # init (see also test_default_factory_with_no_init)
+        @dataclass
+        class C:
+            x: list = field(default_factory=list, init=False)
+        self.assertEqual(astuple(C()), ([],))
+
+        # compare
+        @dataclass
+        class C:
+            x: list = field(default_factory=list, compare=False)
+        self.assertEqual(C(), C([1]))
+
+    def test_default_factory_with_no_init(self):
+        # We need a factory with a side effect.
+        factory = Mock()
+
+        @dataclass
+        class C:
+            x: list = field(default_factory=factory, init=False)
+
+        # Make sure the default factory is called for each new instance.
+        C().x
+        self.assertEqual(factory.call_count, 1)
+        C().x
+        self.assertEqual(factory.call_count, 2)
+
+    def test_default_factory_not_called_if_value_given(self):
+        # We need a factory that we can test if it's been called.
+        factory = Mock()
+
+        @dataclass
+        class C:
+            x: int = field(default_factory=factory)
+
+        # Make sure that if a field has a default factory function,
+        #  it's not called if a value is specified.
+        C().x
+        self.assertEqual(factory.call_count, 1)
+        self.assertEqual(C(10).x, 10)
+        self.assertEqual(factory.call_count, 1)
+        C().x
+        self.assertEqual(factory.call_count, 2)
+
+    def test_default_factory_derived(self):
+        # See bpo-32896.
+        @dataclass
+        class Foo:
+            x: dict = field(default_factory=dict)
+
+        @dataclass
+        class Bar(Foo):
+            y: int = 1
+
+        self.assertEqual(Foo().x, {})
+        self.assertEqual(Bar().x, {})
+        self.assertEqual(Bar().y, 1)
+
+        @dataclass
+        class Baz(Foo):
+            pass
+        self.assertEqual(Baz().x, {})
+
+    def test_intermediate_non_dataclass(self):
+        # Test that an intermediate class that defines
+        #  annotations does not define fields.
+
+        @dataclass
+        class A:
+            x: int
+
+        class B(A):
+            y: int
+
+        @dataclass
+        class C(B):
+            z: int
+
+        c = C(1, 3)
+        self.assertEqual((c.x, c.z), (1, 3))
+
+        # .y was not initialized.
+        with self.assertRaisesRegex(AttributeError,
+                                    'object has no attribute'):
+            c.y
+
+        # And if we again derive a non-dataclass, no fields are added.
+        class D(C):
+            t: int
+        d = D(4, 5)
+        self.assertEqual((d.x, d.z), (4, 5))
+
+    def test_classvar_default_factory(self):
+        # It's an error for a ClassVar to have a factory function.
+        with self.assertRaisesRegex(TypeError,
+                                    'cannot have a default factory'):
+            @dataclass
+            class C:
+                x: ClassVar[int] = field(default_factory=int)
+
+    def test_is_dataclass(self):
+        class NotDataClass:
+            pass
+
+        self.assertFalse(is_dataclass(0))
+        self.assertFalse(is_dataclass(int))
+        self.assertFalse(is_dataclass(NotDataClass))
+        self.assertFalse(is_dataclass(NotDataClass()))
+
+        @dataclass
+        class C:
+            x: int
+
+        @dataclass
+        class D:
+            d: C
+            e: int
+
+        c = C(10)
+        d = D(c, 4)
+
+        self.assertTrue(is_dataclass(C))
+        self.assertTrue(is_dataclass(c))
+        self.assertFalse(is_dataclass(c.x))
+        self.assertTrue(is_dataclass(d.d))
+        self.assertFalse(is_dataclass(d.e))
+
+    def test_is_dataclass_when_getattr_always_returns(self):
+        # See bpo-37868.
+        class A:
+            def __getattr__(self, key):
+                return 0
+        self.assertFalse(is_dataclass(A))
+        a = A()
+
+        # Also test for an instance attribute.
+        class B:
+            pass
+        b = B()
+        b.__dataclass_fields__ = []
+
+        for obj in a, b:
+            with self.subTest(obj=obj):
+                self.assertFalse(is_dataclass(obj))
+
+                # Indirect tests for _is_dataclass_instance().
+                with self.assertRaisesRegex(TypeError, 'should be called on dataclass instances'):
+                    asdict(obj)
+                with self.assertRaisesRegex(TypeError, 'should be called on dataclass instances'):
+                    astuple(obj)
+                with self.assertRaisesRegex(TypeError, 'should be called on dataclass instances'):
+                    replace(obj, x=0)
+
+    def test_is_dataclass_genericalias(self):
+        @dataclass
+        class A(types.GenericAlias):
+            origin: type
+            args: type
+        self.assertTrue(is_dataclass(A))
+        a = A(list, int)
+        self.assertTrue(is_dataclass(type(a)))
+        self.assertTrue(is_dataclass(a))
+
+
+    def test_helper_fields_with_class_instance(self):
+        # Check that we can call fields() on either a class or instance,
+        #  and get back the same thing.
+        @dataclass
+        class C:
+            x: int
+            y: float
+
+        self.assertEqual(fields(C), fields(C(0, 0.0)))
+
+    def test_helper_fields_exception(self):
+        # Check that TypeError is raised if not passed a dataclass or
+        #  instance.
+        with self.assertRaisesRegex(TypeError, 'dataclass type or instance'):
+            fields(0)
+
+        class C: pass
+        with self.assertRaisesRegex(TypeError, 'dataclass type or instance'):
+            fields(C)
+        with self.assertRaisesRegex(TypeError, 'dataclass type or instance'):
+            fields(C())
+
+    def test_clean_traceback_from_fields_exception(self):
+        stdout = io.StringIO()
+        try:
+            fields(object)
+        except TypeError as exc:
+            traceback.print_exception(exc, file=stdout)
+        printed_traceback = stdout.getvalue()
+        self.assertNotIn("AttributeError", printed_traceback)
+        self.assertNotIn("__dataclass_fields__", printed_traceback)
+
+    def test_helper_asdict(self):
+        # Basic tests for asdict(), it should return a new dictionary.
+        @dataclass
+        class C:
+            x: int
+            y: int
+        c = C(1, 2)
+
+        self.assertEqual(asdict(c), {'x': 1, 'y': 2})
+        self.assertEqual(asdict(c), asdict(c))
+        self.assertIsNot(asdict(c), asdict(c))
+        c.x = 42
+        self.assertEqual(asdict(c), {'x': 42, 'y': 2})
+        self.assertIs(type(asdict(c)), dict)
+
+    def test_helper_asdict_raises_on_classes(self):
+        # asdict() should raise on a class object.
+        @dataclass
+        class C:
+            x: int
+            y: int
+        with self.assertRaisesRegex(TypeError, 'dataclass instance'):
+            asdict(C)
+        with self.assertRaisesRegex(TypeError, 'dataclass instance'):
+            asdict(int)
+
+    def test_helper_asdict_copy_values(self):
+        @dataclass
+        class C:
+            x: int
+            y: List[int] = field(default_factory=list)
+        initial = []
+        c = C(1, initial)
+        d = asdict(c)
+        self.assertEqual(d['y'], initial)
+        self.assertIsNot(d['y'], initial)
+        c = C(1)
+        d = asdict(c)
+        d['y'].append(1)
+        self.assertEqual(c.y, [])
+
+    def test_helper_asdict_nested(self):
+        @dataclass
+        class UserId:
+            token: int
+            group: int
+        @dataclass
+        class User:
+            name: str
+            id: UserId
+        u = User('Joe', UserId(123, 1))
+        d = asdict(u)
+        self.assertEqual(d, {'name': 'Joe', 'id': {'token': 123, 'group': 1}})
+        self.assertIsNot(asdict(u), asdict(u))
+        u.id.group = 2
+        self.assertEqual(asdict(u), {'name': 'Joe',
+                                     'id': {'token': 123, 'group': 2}})
+
+    def test_helper_asdict_builtin_containers(self):
+        @dataclass
+        class User:
+            name: str
+            id: int
+        @dataclass
+        class GroupList:
+            id: int
+            users: List[User]
+        @dataclass
+        class GroupTuple:
+            id: int
+            users: Tuple[User, ...]
+        @dataclass
+        class GroupDict:
+            id: int
+            users: Dict[str, User]
+        a = User('Alice', 1)
+        b = User('Bob', 2)
+        gl = GroupList(0, [a, b])
+        gt = GroupTuple(0, (a, b))
+        gd = GroupDict(0, {'first': a, 'second': b})
+        self.assertEqual(asdict(gl), {'id': 0, 'users': [{'name': 'Alice', 'id': 1},
+                                                         {'name': 'Bob', 'id': 2}]})
+        self.assertEqual(asdict(gt), {'id': 0, 'users': ({'name': 'Alice', 'id': 1},
+                                                         {'name': 'Bob', 'id': 2})})
+        self.assertEqual(asdict(gd), {'id': 0, 'users': {'first': {'name': 'Alice', 'id': 1},
+                                                         'second': {'name': 'Bob', 'id': 2}}})
+
+    def test_helper_asdict_builtin_object_containers(self):
+        @dataclass
+        class Child:
+            d: object
+
+        @dataclass
+        class Parent:
+            child: Child
+
+        self.assertEqual(asdict(Parent(Child([1]))), {'child': {'d': [1]}})
+        self.assertEqual(asdict(Parent(Child({1: 2}))), {'child': {'d': {1: 2}}})
+
+    def test_helper_asdict_factory(self):
+        @dataclass
+        class C:
+            x: int
+            y: int
+        c = C(1, 2)
+        d = asdict(c, dict_factory=OrderedDict)
+        self.assertEqual(d, OrderedDict([('x', 1), ('y', 2)]))
+        self.assertIsNot(d, asdict(c, dict_factory=OrderedDict))
+        c.x = 42
+        d = asdict(c, dict_factory=OrderedDict)
+        self.assertEqual(d, OrderedDict([('x', 42), ('y', 2)]))
+        self.assertIs(type(d), OrderedDict)
+
+    def test_helper_asdict_namedtuple(self):
+        T = namedtuple('T', 'a b c')
+        @dataclass
+        class C:
+            x: str
+            y: T
+        c = C('outer', T(1, C('inner', T(11, 12, 13)), 2))
+
+        d = asdict(c)
+        self.assertEqual(d, {'x': 'outer',
+                             'y': T(1,
+                                    {'x': 'inner',
+                                     'y': T(11, 12, 13)},
+                                    2),
+                             }
+                         )
+
+        # Now with a dict_factory.  OrderedDict is convenient, but
+        # since it compares to dicts, we also need to have separate
+        # assertIs tests.
+        d = asdict(c, dict_factory=OrderedDict)
+        self.assertEqual(d, {'x': 'outer',
+                             'y': T(1,
+                                    {'x': 'inner',
+                                     'y': T(11, 12, 13)},
+                                    2),
+                             }
+                         )
+
+        # Make sure that the returned dicts are actually OrderedDicts.
+        self.assertIs(type(d), OrderedDict)
+        self.assertIs(type(d['y'][1]), OrderedDict)
+
+    def test_helper_asdict_namedtuple_key(self):
+        # Ensure that a field that contains a dict which has a
+        # namedtuple as a key works with asdict().
+
+        @dataclass
+        class C:
+            f: dict
+        T = namedtuple('T', 'a')
+
+        c = C({T('an a'): 0})
+
+        self.assertEqual(asdict(c), {'f': {T(a='an a'): 0}})
+
+    def test_helper_asdict_namedtuple_derived(self):
+        class T(namedtuple('Tbase', 'a')):
+            def my_a(self):
+                return self.a
+
+        @dataclass
+        class C:
+            f: T
+
+        t = T(6)
+        c = C(t)
+
+        d = asdict(c)
+        self.assertEqual(d, {'f': T(a=6)})
+        # Make sure that t has been copied, not used directly.
+        self.assertIsNot(d['f'], t)
+        self.assertEqual(d['f'].my_a(), 6)
+
+    def test_helper_asdict_defaultdict(self):
+        # Ensure asdict() does not throw exceptions when a
+        # defaultdict is a member of a dataclass
+        @dataclass
+        class C:
+            mp: DefaultDict[str, List]
+
+        dd = defaultdict(list)
+        dd["x"].append(12)
+        c = C(mp=dd)
+        d = asdict(c)
+
+        self.assertEqual(d, {"mp": {"x": [12]}})
+        self.assertTrue(d["mp"] is not c.mp)  # make sure defaultdict is copied
+
+    def test_helper_astuple(self):
+        # Basic tests for astuple(), it should return a new tuple.
+        @dataclass
+        class C:
+            x: int
+            y: int = 0
+        c = C(1)
+
+        self.assertEqual(astuple(c), (1, 0))
+        self.assertEqual(astuple(c), astuple(c))
+        self.assertIsNot(astuple(c), astuple(c))
+        c.y = 42
+        self.assertEqual(astuple(c), (1, 42))
+        self.assertIs(type(astuple(c)), tuple)
+
+    def test_helper_astuple_raises_on_classes(self):
+        # astuple() should raise on a class object.
+        @dataclass
+        class C:
+            x: int
+            y: int
+        with self.assertRaisesRegex(TypeError, 'dataclass instance'):
+            astuple(C)
+        with self.assertRaisesRegex(TypeError, 'dataclass instance'):
+            astuple(int)
+
+    def test_helper_astuple_copy_values(self):
+        @dataclass
+        class C:
+            x: int
+            y: List[int] = field(default_factory=list)
+        initial = []
+        c = C(1, initial)
+        t = astuple(c)
+        self.assertEqual(t[1], initial)
+        self.assertIsNot(t[1], initial)
+        c = C(1)
+        t = astuple(c)
+        t[1].append(1)
+        self.assertEqual(c.y, [])
+
+    def test_helper_astuple_nested(self):
+        @dataclass
+        class UserId:
+            token: int
+            group: int
+        @dataclass
+        class User:
+            name: str
+            id: UserId
+        u = User('Joe', UserId(123, 1))
+        t = astuple(u)
+        self.assertEqual(t, ('Joe', (123, 1)))
+        self.assertIsNot(astuple(u), astuple(u))
+        u.id.group = 2
+        self.assertEqual(astuple(u), ('Joe', (123, 2)))
+
+    def test_helper_astuple_builtin_containers(self):
+        @dataclass
+        class User:
+            name: str
+            id: int
+        @dataclass
+        class GroupList:
+            id: int
+            users: List[User]
+        @dataclass
+        class GroupTuple:
+            id: int
+            users: Tuple[User, ...]
+        @dataclass
+        class GroupDict:
+            id: int
+            users: Dict[str, User]
+        a = User('Alice', 1)
+        b = User('Bob', 2)
+        gl = GroupList(0, [a, b])
+        gt = GroupTuple(0, (a, b))
+        gd = GroupDict(0, {'first': a, 'second': b})
+        self.assertEqual(astuple(gl), (0, [('Alice', 1), ('Bob', 2)]))
+        self.assertEqual(astuple(gt), (0, (('Alice', 1), ('Bob', 2))))
+        self.assertEqual(astuple(gd), (0, {'first': ('Alice', 1), 'second': ('Bob', 2)}))
+
+    def test_helper_astuple_builtin_object_containers(self):
+        @dataclass
+        class Child:
+            d: object
+
+        @dataclass
+        class Parent:
+            child: Child
+
+        self.assertEqual(astuple(Parent(Child([1]))), (([1],),))
+        self.assertEqual(astuple(Parent(Child({1: 2}))), (({1: 2},),))
+
+    def test_helper_astuple_factory(self):
+        @dataclass
+        class C:
+            x: int
+            y: int
+        NT = namedtuple('NT', 'x y')
+        def nt(lst):
+            return NT(*lst)
+        c = C(1, 2)
+        t = astuple(c, tuple_factory=nt)
+        self.assertEqual(t, NT(1, 2))
+        self.assertIsNot(t, astuple(c, tuple_factory=nt))
+        c.x = 42
+        t = astuple(c, tuple_factory=nt)
+        self.assertEqual(t, NT(42, 2))
+        self.assertIs(type(t), NT)
+
+    def test_helper_astuple_namedtuple(self):
+        T = namedtuple('T', 'a b c')
+        @dataclass
+        class C:
+            x: str
+            y: T
+        c = C('outer', T(1, C('inner', T(11, 12, 13)), 2))
+
+        t = astuple(c)
+        self.assertEqual(t, ('outer', T(1, ('inner', (11, 12, 13)), 2)))
+
+        # Now, using a tuple_factory.  list is convenient here.
+        t = astuple(c, tuple_factory=list)
+        self.assertEqual(t, ['outer', T(1, ['inner', T(11, 12, 13)], 2)])
+
+    def test_helper_astuple_defaultdict(self):
+        # Ensure astuple() does not throw exceptions when a
+        # defaultdict is a member of a dataclass
+        @dataclass
+        class C:
+            mp: DefaultDict[str, List]
+
+        dd = defaultdict(list)
+        dd["x"].append(12)
+        c = C(mp=dd)
+        t = astuple(c)
+
+        self.assertEqual(t, ({"x": [12]},))
+        self.assertTrue(t[0] is not dd) # make sure defaultdict is copied
+
+    def test_dynamic_class_creation(self):
+        cls_dict = {'__annotations__': {'x': int, 'y': int},
+                    }
+
+        # Create the class.
+        cls = type('C', (), cls_dict)
+
+        # Make it a dataclass.
+        cls1 = dataclass(cls)
+
+        self.assertEqual(cls1, cls)
+        self.assertEqual(asdict(cls(1, 2)), {'x': 1, 'y': 2})
+
+    def test_dynamic_class_creation_using_field(self):
+        cls_dict = {'__annotations__': {'x': int, 'y': int},
+                    'y': field(default=5),
+                    }
+
+        # Create the class.
+        cls = type('C', (), cls_dict)
+
+        # Make it a dataclass.
+        cls1 = dataclass(cls)
+
+        self.assertEqual(cls1, cls)
+        self.assertEqual(asdict(cls1(1)), {'x': 1, 'y': 5})
+
+    def test_init_in_order(self):
+        @dataclass
+        class C:
+            a: int
+            b: int = field()
+            c: list = field(default_factory=list, init=False)
+            d: list = field(default_factory=list)
+            e: int = field(default=4, init=False)
+            f: int = 4
+
+        calls = []
+        def setattr(self, name, value):
+            calls.append((name, value))
+
+        C.__setattr__ = setattr
+        c = C(0, 1)
+        self.assertEqual(('a', 0), calls[0])
+        self.assertEqual(('b', 1), calls[1])
+        self.assertEqual(('c', []), calls[2])
+        self.assertEqual(('d', []), calls[3])
+        self.assertNotIn(('e', 4), calls)
+        self.assertEqual(('f', 4), calls[4])
+
+    def test_items_in_dicts(self):
+        @dataclass
+        class C:
+            a: int
+            b: list = field(default_factory=list, init=False)
+            c: list = field(default_factory=list)
+            d: int = field(default=4, init=False)
+            e: int = 0
+
+        c = C(0)
+        # Class dict
+        self.assertNotIn('a', C.__dict__)
+        self.assertNotIn('b', C.__dict__)
+        self.assertNotIn('c', C.__dict__)
+        self.assertIn('d', C.__dict__)
+        self.assertEqual(C.d, 4)
+        self.assertIn('e', C.__dict__)
+        self.assertEqual(C.e, 0)
+        # Instance dict
+        self.assertIn('a', c.__dict__)
+        self.assertEqual(c.a, 0)
+        self.assertIn('b', c.__dict__)
+        self.assertEqual(c.b, [])
+        self.assertIn('c', c.__dict__)
+        self.assertEqual(c.c, [])
+        self.assertNotIn('d', c.__dict__)
+        self.assertIn('e', c.__dict__)
+        self.assertEqual(c.e, 0)
+
+    def test_alternate_classmethod_constructor(self):
+        # Since __post_init__ can't take params, use a classmethod
+        #  alternate constructor.  This is mostly an example to show
+        #  how to use this technique.
+        @dataclass
+        class C:
+            x: int
+            @classmethod
+            def from_file(cls, filename):
+                # In a real example, create a new instance
+                #  and populate 'x' from contents of a file.
+                value_in_file = 20
+                return cls(value_in_file)
+
+        self.assertEqual(C.from_file('filename').x, 20)
+
+    def test_field_metadata_default(self):
+        # Make sure the default metadata is read-only and of
+        #  zero length.
+        @dataclass
+        class C:
+            i: int
+
+        self.assertFalse(fields(C)[0].metadata)
+        self.assertEqual(len(fields(C)[0].metadata), 0)
+        with self.assertRaisesRegex(TypeError,
+                                    'does not support item assignment'):
+            fields(C)[0].metadata['test'] = 3
+
+    def test_field_metadata_mapping(self):
+        # Make sure only a mapping can be passed as metadata
+        #  zero length.
+        with self.assertRaises(TypeError):
+            @dataclass
+            class C:
+                i: int = field(metadata=0)
+
+        # Make sure an empty dict works.
+        d = {}
+        @dataclass
+        class C:
+            i: int = field(metadata=d)
+        self.assertFalse(fields(C)[0].metadata)
+        self.assertEqual(len(fields(C)[0].metadata), 0)
+        # Update should work (see bpo-35960).
+        d['foo'] = 1
+        self.assertEqual(len(fields(C)[0].metadata), 1)
+        self.assertEqual(fields(C)[0].metadata['foo'], 1)
+        with self.assertRaisesRegex(TypeError,
+                                    'does not support item assignment'):
+            fields(C)[0].metadata['test'] = 3
+
+        # Make sure a non-empty dict works.
+        d = {'test': 10, 'bar': '42', 3: 'three'}
+        @dataclass
+        class C:
+            i: int = field(metadata=d)
+        self.assertEqual(len(fields(C)[0].metadata), 3)
+        self.assertEqual(fields(C)[0].metadata['test'], 10)
+        self.assertEqual(fields(C)[0].metadata['bar'], '42')
+        self.assertEqual(fields(C)[0].metadata[3], 'three')
+        # Update should work.
+        d['foo'] = 1
+        self.assertEqual(len(fields(C)[0].metadata), 4)
+        self.assertEqual(fields(C)[0].metadata['foo'], 1)
+        with self.assertRaises(KeyError):
+            # Non-existent key.
+            fields(C)[0].metadata['baz']
+        with self.assertRaisesRegex(TypeError,
+                                    'does not support item assignment'):
+            fields(C)[0].metadata['test'] = 3
+
+    def test_field_metadata_custom_mapping(self):
+        # Try a custom mapping.
+        class SimpleNameSpace:
+            def __init__(self, **kw):
+                self.__dict__.update(kw)
+
+            def __getitem__(self, item):
+                if item == 'xyzzy':
+                    return 'plugh'
+                return getattr(self, item)
+
+            def __len__(self):
+                return self.__dict__.__len__()
+
+        @dataclass
+        class C:
+            i: int = field(metadata=SimpleNameSpace(a=10))
+
+        self.assertEqual(len(fields(C)[0].metadata), 1)
+        self.assertEqual(fields(C)[0].metadata['a'], 10)
+        with self.assertRaises(AttributeError):
+            fields(C)[0].metadata['b']
+        # Make sure we're still talking to our custom mapping.
+        self.assertEqual(fields(C)[0].metadata['xyzzy'], 'plugh')
+
+    def test_generic_dataclasses(self):
+        T = TypeVar('T')
+
+        @dataclass
+        class LabeledBox(Generic[T]):
+            content: T
+            label: str = '<unknown>'
+
+        box = LabeledBox(42)
+        self.assertEqual(box.content, 42)
+        self.assertEqual(box.label, '<unknown>')
+
+        # Subscripting the resulting class should work, etc.
+        Alias = List[LabeledBox[int]]
+
+    def test_generic_extending(self):
+        S = TypeVar('S')
+        T = TypeVar('T')
+
+        @dataclass
+        class Base(Generic[T, S]):
+            x: T
+            y: S
+
+        @dataclass
+        class DataDerived(Base[int, T]):
+            new_field: str
+        Alias = DataDerived[str]
+        c = Alias(0, 'test1', 'test2')
+        self.assertEqual(astuple(c), (0, 'test1', 'test2'))
+
+        class NonDataDerived(Base[int, T]):
+            def new_method(self):
+                return self.y
+        Alias = NonDataDerived[float]
+        c = Alias(10, 1.0)
+        self.assertEqual(c.new_method(), 1.0)
+
+    def test_generic_dynamic(self):
+        T = TypeVar('T')
+
+        @dataclass
+        class Parent(Generic[T]):
+            x: T
+        Child = make_dataclass('Child', [('y', T), ('z', Optional[T], None)],
+                               bases=(Parent[int], Generic[T]), namespace={'other': 42})
+        self.assertIs(Child[int](1, 2).z, None)
+        self.assertEqual(Child[int](1, 2, 3).z, 3)
+        self.assertEqual(Child[int](1, 2, 3).other, 42)
+        # Check that type aliases work correctly.
+        Alias = Child[T]
+        self.assertEqual(Alias[int](1, 2).x, 1)
+        # Check MRO resolution.
+        self.assertEqual(Child.__mro__, (Child, Parent, Generic, object))
+
+    def test_dataclasses_pickleable(self):
+        global P, Q, R
+        @dataclass
+        class P:
+            x: int
+            y: int = 0
+        @dataclass
+        class Q:
+            x: int
+            y: int = field(default=0, init=False)
+        @dataclass
+        class R:
+            x: int
+            y: List[int] = field(default_factory=list)
+        q = Q(1)
+        q.y = 2
+        samples = [P(1), P(1, 2), Q(1), q, R(1), R(1, [2, 3, 4])]
+        for sample in samples:
+            for proto in range(pickle.HIGHEST_PROTOCOL + 1):
+                with self.subTest(sample=sample, proto=proto):
+                    new_sample = pickle.loads(pickle.dumps(sample, proto))
+                    self.assertEqual(sample.x, new_sample.x)
+                    self.assertEqual(sample.y, new_sample.y)
+                    self.assertIsNot(sample, new_sample)
+                    new_sample.x = 42
+                    another_new_sample = pickle.loads(pickle.dumps(new_sample, proto))
+                    self.assertEqual(new_sample.x, another_new_sample.x)
+                    self.assertEqual(sample.y, another_new_sample.y)
+
+    def test_dataclasses_qualnames(self):
+        @dataclass(order=True, unsafe_hash=True, frozen=True)
+        class A:
+            x: int
+            y: int
+
+        self.assertEqual(A.__init__.__name__, "__init__")
+        for function in (
+            '__eq__',
+            '__lt__',
+            '__le__',
+            '__gt__',
+            '__ge__',
+            '__hash__',
+            '__init__',
+            '__repr__',
+            '__setattr__',
+            '__delattr__',
+        ):
+            self.assertEqual(getattr(A, function).__qualname__, f"TestCase.test_dataclasses_qualnames.<locals>.A.{function}")
+
+        with self.assertRaisesRegex(TypeError, r"A\.__init__\(\) missing"):
+            A()
+
+
+class TestFieldNoAnnotation(unittest.TestCase):
+    def test_field_without_annotation(self):
+        with self.assertRaisesRegex(TypeError,
+                                    "'f' is a field but has no type annotation"):
+            @dataclass
+            class C:
+                f = field()
+
+    def test_field_without_annotation_but_annotation_in_base(self):
+        @dataclass
+        class B:
+            f: int
+
+        with self.assertRaisesRegex(TypeError,
+                                    "'f' is a field but has no type annotation"):
+            # This is still an error: make sure we don't pick up the
+            #  type annotation in the base class.
+            @dataclass
+            class C(B):
+                f = field()
+
+    def test_field_without_annotation_but_annotation_in_base_not_dataclass(self):
+        # Same test, but with the base class not a dataclass.
+        class B:
+            f: int
+
+        with self.assertRaisesRegex(TypeError,
+                                    "'f' is a field but has no type annotation"):
+            # This is still an error: make sure we don't pick up the
+            #  type annotation in the base class.
+            @dataclass
+            class C(B):
+                f = field()
+
+
+class TestDocString(unittest.TestCase):
+    def assertDocStrEqual(self, a, b):
+        # Because 3.6 and 3.7 differ in how inspect.signature work
+        #  (see bpo #32108), for the time being just compare them with
+        #  whitespace stripped.
+        self.assertEqual(a.replace(' ', ''), b.replace(' ', ''))
+
+    def test_existing_docstring_not_overridden(self):
+        @dataclass
+        class C:
+            """Lorem ipsum"""
+            x: int
+
+        self.assertEqual(C.__doc__, "Lorem ipsum")
+
+    def test_docstring_no_fields(self):
+        @dataclass
+        class C:
+            pass
+
+        self.assertDocStrEqual(C.__doc__, "C()")
+
+    def test_docstring_one_field(self):
+        @dataclass
+        class C:
+            x: int
+
+        self.assertDocStrEqual(C.__doc__, "C(x:int)")
+
+    def test_docstring_two_fields(self):
+        @dataclass
+        class C:
+            x: int
+            y: int
+
+        self.assertDocStrEqual(C.__doc__, "C(x:int, y:int)")
+
+    def test_docstring_three_fields(self):
+        @dataclass
+        class C:
+            x: int
+            y: int
+            z: str
+
+        self.assertDocStrEqual(C.__doc__, "C(x:int, y:int, z:str)")
+
+    def test_docstring_one_field_with_default(self):
+        @dataclass
+        class C:
+            x: int = 3
+
+        self.assertDocStrEqual(C.__doc__, "C(x:int=3)")
+
+    def test_docstring_one_field_with_default_none(self):
+        @dataclass
+        class C:
+            x: Union[int, type(None)] = None
+
+        self.assertDocStrEqual(C.__doc__, "C(x:Optional[int]=None)")
+
+    def test_docstring_list_field(self):
+        @dataclass
+        class C:
+            x: List[int]
+
+        self.assertDocStrEqual(C.__doc__, "C(x:List[int])")
+
+    def test_docstring_list_field_with_default_factory(self):
+        @dataclass
+        class C:
+            x: List[int] = field(default_factory=list)
+
+        self.assertDocStrEqual(C.__doc__, "C(x:List[int]=<factory>)")
+
+    def test_docstring_deque_field(self):
+        @dataclass
+        class C:
+            x: deque
+
+        self.assertDocStrEqual(C.__doc__, "C(x:collections.deque)")
+
+    def test_docstring_deque_field_with_default_factory(self):
+        @dataclass
+        class C:
+            x: deque = field(default_factory=deque)
+
+        self.assertDocStrEqual(C.__doc__, "C(x:collections.deque=<factory>)")
+
+    def test_docstring_with_no_signature(self):
+        # See https://github.com/python/cpython/issues/103449
+        class Meta(type):
+            __call__ = dict
+        class Base(metaclass=Meta):
+            pass
+
+        @dataclass
+        class C(Base):
+            pass
+
+        self.assertDocStrEqual(C.__doc__, "C")
+
+
+class TestInit(unittest.TestCase):
+    def test_base_has_init(self):
+        class B:
+            def __init__(self):
+                self.z = 100
+
+        # Make sure that declaring this class doesn't raise an error.
+        #  The issue is that we can't override __init__ in our class,
+        #  but it should be okay to add __init__ to us if our base has
+        #  an __init__.
+        @dataclass
+        class C(B):
+            x: int = 0
+        c = C(10)
+        self.assertEqual(c.x, 10)
+        self.assertNotIn('z', vars(c))
+
+        # Make sure that if we don't add an init, the base __init__
+        #  gets called.
+        @dataclass(init=False)
+        class C(B):
+            x: int = 10
+        c = C()
+        self.assertEqual(c.x, 10)
+        self.assertEqual(c.z, 100)
+
+    def test_no_init(self):
+        @dataclass(init=False)
+        class C:
+            i: int = 0
+        self.assertEqual(C().i, 0)
+
+        @dataclass(init=False)
+        class C:
+            i: int = 2
+            def __init__(self):
+                self.i = 3
+        self.assertEqual(C().i, 3)
+
+    def test_overwriting_init(self):
+        # If the class has __init__, use it no matter the value of
+        #  init=.
+
+        @dataclass
+        class C:
+            x: int
+            def __init__(self, x):
+                self.x = 2 * x
+        self.assertEqual(C(3).x, 6)
+
+        @dataclass(init=True)
+        class C:
+            x: int
+            def __init__(self, x):
+                self.x = 2 * x
+        self.assertEqual(C(4).x, 8)
+
+        @dataclass(init=False)
+        class C:
+            x: int
+            def __init__(self, x):
+                self.x = 2 * x
+        self.assertEqual(C(5).x, 10)
+
+    def test_inherit_from_protocol(self):
+        # Dataclasses inheriting from protocol should preserve their own `__init__`.
+        # See bpo-45081.
+
+        class P(Protocol):
+            a: int
+
+        @dataclass
+        class C(P):
+            a: int
+
+        self.assertEqual(C(5).a, 5)
+
+        @dataclass
+        class D(P):
+            def __init__(self, a):
+                self.a = a * 2
+
+        self.assertEqual(D(5).a, 10)
+
+
+class TestRepr(unittest.TestCase):
+    def test_repr(self):
+        @dataclass
+        class B:
+            x: int
+
+        @dataclass
+        class C(B):
+            y: int = 10
+
+        o = C(4)
+        self.assertEqual(repr(o), 'TestRepr.test_repr.<locals>.C(x=4, y=10)')
+
+        @dataclass
+        class D(C):
+            x: int = 20
+        self.assertEqual(repr(D()), 'TestRepr.test_repr.<locals>.D(x=20, y=10)')
+
+        @dataclass
+        class C:
+            @dataclass
+            class D:
+                i: int
+            @dataclass
+            class E:
+                pass
+        self.assertEqual(repr(C.D(0)), 'TestRepr.test_repr.<locals>.C.D(i=0)')
+        self.assertEqual(repr(C.E()), 'TestRepr.test_repr.<locals>.C.E()')
+
+    def test_no_repr(self):
+        # Test a class with no __repr__ and repr=False.
+        @dataclass(repr=False)
+        class C:
+            x: int
+        self.assertIn(f'{__name__}.TestRepr.test_no_repr.<locals>.C object at',
+                      repr(C(3)))
+
+        # Test a class with a __repr__ and repr=False.
+        @dataclass(repr=False)
+        class C:
+            x: int
+            def __repr__(self):
+                return 'C-class'
+        self.assertEqual(repr(C(3)), 'C-class')
+
+    def test_overwriting_repr(self):
+        # If the class has __repr__, use it no matter the value of
+        #  repr=.
+
+        @dataclass
+        class C:
+            x: int
+            def __repr__(self):
+                return 'x'
+        self.assertEqual(repr(C(0)), 'x')
+
+        @dataclass(repr=True)
+        class C:
+            x: int
+            def __repr__(self):
+                return 'x'
+        self.assertEqual(repr(C(0)), 'x')
+
+        @dataclass(repr=False)
+        class C:
+            x: int
+            def __repr__(self):
+                return 'x'
+        self.assertEqual(repr(C(0)), 'x')
+
+
+class TestEq(unittest.TestCase):
+    def test_no_eq(self):
+        # Test a class with no __eq__ and eq=False.
+        @dataclass(eq=False)
+        class C:
+            x: int
+        self.assertNotEqual(C(0), C(0))
+        c = C(3)
+        self.assertEqual(c, c)
+
+        # Test a class with an __eq__ and eq=False.
+        @dataclass(eq=False)
+        class C:
+            x: int
+            def __eq__(self, other):
+                return other == 10
+        self.assertEqual(C(3), 10)
+
+    def test_overwriting_eq(self):
+        # If the class has __eq__, use it no matter the value of
+        #  eq=.
+
+        @dataclass
+        class C:
+            x: int
+            def __eq__(self, other):
+                return other == 3
+        self.assertEqual(C(1), 3)
+        self.assertNotEqual(C(1), 1)
+
+        @dataclass(eq=True)
+        class C:
+            x: int
+            def __eq__(self, other):
+                return other == 4
+        self.assertEqual(C(1), 4)
+        self.assertNotEqual(C(1), 1)
+
+        @dataclass(eq=False)
+        class C:
+            x: int
+            def __eq__(self, other):
+                return other == 5
+        self.assertEqual(C(1), 5)
+        self.assertNotEqual(C(1), 1)
+
+
+class TestOrdering(unittest.TestCase):
+    def test_functools_total_ordering(self):
+        # Test that functools.total_ordering works with this class.
+        @total_ordering
+        @dataclass
+        class C:
+            x: int
+            def __lt__(self, other):
+                # Perform the test "backward", just to make
+                #  sure this is being called.
+                return self.x >= other
+
+        self.assertLess(C(0), -1)
+        self.assertLessEqual(C(0), -1)
+        self.assertGreater(C(0), 1)
+        self.assertGreaterEqual(C(0), 1)
+
+    def test_no_order(self):
+        # Test that no ordering functions are added by default.
+        @dataclass(order=False)
+        class C:
+            x: int
+        # Make sure no order methods are added.
+        self.assertNotIn('__le__', C.__dict__)
+        self.assertNotIn('__lt__', C.__dict__)
+        self.assertNotIn('__ge__', C.__dict__)
+        self.assertNotIn('__gt__', C.__dict__)
+
+        # Test that __lt__ is still called
+        @dataclass(order=False)
+        class C:
+            x: int
+            def __lt__(self, other):
+                return False
+        # Make sure other methods aren't added.
+        self.assertNotIn('__le__', C.__dict__)
+        self.assertNotIn('__ge__', C.__dict__)
+        self.assertNotIn('__gt__', C.__dict__)
+
+    def test_overwriting_order(self):
+        with self.assertRaisesRegex(TypeError,
+                                    'Cannot overwrite attribute __lt__'
+                                    '.*using functools.total_ordering'):
+            @dataclass(order=True)
+            class C:
+                x: int
+                def __lt__(self):
+                    pass
+
+        with self.assertRaisesRegex(TypeError,
+                                    'Cannot overwrite attribute __le__'
+                                    '.*using functools.total_ordering'):
+            @dataclass(order=True)
+            class C:
+                x: int
+                def __le__(self):
+                    pass
+
+        with self.assertRaisesRegex(TypeError,
+                                    'Cannot overwrite attribute __gt__'
+                                    '.*using functools.total_ordering'):
+            @dataclass(order=True)
+            class C:
+                x: int
+                def __gt__(self):
+                    pass
+
+        with self.assertRaisesRegex(TypeError,
+                                    'Cannot overwrite attribute __ge__'
+                                    '.*using functools.total_ordering'):
+            @dataclass(order=True)
+            class C:
+                x: int
+                def __ge__(self):
+                    pass
+
+class TestHash(unittest.TestCase):
+    def test_unsafe_hash(self):
+        @dataclass(unsafe_hash=True)
+        class C:
+            x: int
+            y: str
+        self.assertEqual(hash(C(1, 'foo')), hash((1, 'foo')))
+
+    def test_hash_rules(self):
+        def non_bool(value):
+            # Map to something else that's True, but not a bool.
+            if value is None:
+                return None
+            if value:
+                return (3,)
+            return 0
+
+        def test(case, unsafe_hash, eq, frozen, with_hash, result):
+            with self.subTest(case=case, unsafe_hash=unsafe_hash, eq=eq,
+                              frozen=frozen):
+                if result != 'exception':
+                    if with_hash:
+                        @dataclass(unsafe_hash=unsafe_hash, eq=eq, frozen=frozen)
+                        class C:
+                            def __hash__(self):
+                                return 0
+                    else:
+                        @dataclass(unsafe_hash=unsafe_hash, eq=eq, frozen=frozen)
+                        class C:
+                            pass
+
+                # See if the result matches what's expected.
+                if result == 'fn':
+                    # __hash__ contains the function we generated.
+                    self.assertIn('__hash__', C.__dict__)
+                    self.assertIsNotNone(C.__dict__['__hash__'])
+
+                elif result == '':
+                    # __hash__ is not present in our class.
+                    if not with_hash:
+                        self.assertNotIn('__hash__', C.__dict__)
+
+                elif result == 'none':
+                    # __hash__ is set to None.
+                    self.assertIn('__hash__', C.__dict__)
+                    self.assertIsNone(C.__dict__['__hash__'])
+
+                elif result == 'exception':
+                    # Creating the class should cause an exception.
+                    #  This only happens with with_hash==True.
+                    assert(with_hash)
+                    with self.assertRaisesRegex(TypeError, 'Cannot overwrite attribute __hash__'):
+                        @dataclass(unsafe_hash=unsafe_hash, eq=eq, frozen=frozen)
+                        class C:
+                            def __hash__(self):
+                                return 0
+
+                else:
+                    assert False, f'unknown result {result!r}'
+
+        # There are 8 cases of:
+        #  unsafe_hash=True/False
+        #  eq=True/False
+        #  frozen=True/False
+        # And for each of these, a different result if
+        #  __hash__ is defined or not.
+        for case, (unsafe_hash,  eq,    frozen, res_no_defined_hash, res_defined_hash) in enumerate([
+                  (False,        False, False,  '',                  ''),
+                  (False,        False, True,   '',                  ''),
+                  (False,        True,  False,  'none',              ''),
+                  (False,        True,  True,   'fn',                ''),
+                  (True,         False, False,  'fn',                'exception'),
+                  (True,         False, True,   'fn',                'exception'),
+                  (True,         True,  False,  'fn',                'exception'),
+                  (True,         True,  True,   'fn',                'exception'),
+                  ], 1):
+            test(case, unsafe_hash, eq, frozen, False, res_no_defined_hash)
+            test(case, unsafe_hash, eq, frozen, True,  res_defined_hash)
+
+            # Test non-bool truth values, too.  This is just to
+            #  make sure the data-driven table in the decorator
+            #  handles non-bool values.
+            test(case, non_bool(unsafe_hash), non_bool(eq), non_bool(frozen), False, res_no_defined_hash)
+            test(case, non_bool(unsafe_hash), non_bool(eq), non_bool(frozen), True,  res_defined_hash)
+
+
+    def test_eq_only(self):
+        # If a class defines __eq__, __hash__ is automatically added
+        #  and set to None.  This is normal Python behavior, not
+        #  related to dataclasses.  Make sure we don't interfere with
+        #  that (see bpo=32546).
+
+        @dataclass
+        class C:
+            i: int
+            def __eq__(self, other):
+                return self.i == other.i
+        self.assertEqual(C(1), C(1))
+        self.assertNotEqual(C(1), C(4))
+
+        # And make sure things work in this case if we specify
+        #  unsafe_hash=True.
+        @dataclass(unsafe_hash=True)
+        class C:
+            i: int
+            def __eq__(self, other):
+                return self.i == other.i
+        self.assertEqual(C(1), C(1.0))
+        self.assertEqual(hash(C(1)), hash(C(1.0)))
+
+        # And check that the classes __eq__ is being used, despite
+        #  specifying eq=True.
+        @dataclass(unsafe_hash=True, eq=True)
+        class C:
+            i: int
+            def __eq__(self, other):
+                return self.i == 3 and self.i == other.i
+        self.assertEqual(C(3), C(3))
+        self.assertNotEqual(C(1), C(1))
+        self.assertEqual(hash(C(1)), hash(C(1.0)))
+
+    def test_0_field_hash(self):
+        @dataclass(frozen=True)
+        class C:
+            pass
+        self.assertEqual(hash(C()), hash(()))
+
+        @dataclass(unsafe_hash=True)
+        class C:
+            pass
+        self.assertEqual(hash(C()), hash(()))
+
+    def test_1_field_hash(self):
+        @dataclass(frozen=True)
+        class C:
+            x: int
+        self.assertEqual(hash(C(4)), hash((4,)))
+        self.assertEqual(hash(C(42)), hash((42,)))
+
+        @dataclass(unsafe_hash=True)
+        class C:
+            x: int
+        self.assertEqual(hash(C(4)), hash((4,)))
+        self.assertEqual(hash(C(42)), hash((42,)))
+
+    def test_hash_no_args(self):
+        # Test dataclasses with no hash= argument.  This exists to
+        #  make sure that if the @dataclass parameter name is changed
+        #  or the non-default hashing behavior changes, the default
+        #  hashability keeps working the same way.
+
+        class Base:
+            def __hash__(self):
+                return 301
+
+        # If frozen or eq is None, then use the default value (do not
+        #  specify any value in the decorator).
+        for frozen, eq,    base,   expected       in [
+            (None,  None,  object, 'unhashable'),
+            (None,  None,  Base,   'unhashable'),
+            (None,  False, object, 'object'),
+            (None,  False, Base,   'base'),
+            (None,  True,  object, 'unhashable'),
+            (None,  True,  Base,   'unhashable'),
+            (False, None,  object, 'unhashable'),
+            (False, None,  Base,   'unhashable'),
+            (False, False, object, 'object'),
+            (False, False, Base,   'base'),
+            (False, True,  object, 'unhashable'),
+            (False, True,  Base,   'unhashable'),
+            (True,  None,  object, 'tuple'),
+            (True,  None,  Base,   'tuple'),
+            (True,  False, object, 'object'),
+            (True,  False, Base,   'base'),
+            (True,  True,  object, 'tuple'),
+            (True,  True,  Base,   'tuple'),
+            ]:
+
+            with self.subTest(frozen=frozen, eq=eq, base=base, expected=expected):
+                # First, create the class.
+                if frozen is None and eq is None:
+                    @dataclass
+                    class C(base):
+                        i: int
+                elif frozen is None:
+                    @dataclass(eq=eq)
+                    class C(base):
+                        i: int
+                elif eq is None:
+                    @dataclass(frozen=frozen)
+                    class C(base):
+                        i: int
+                else:
+                    @dataclass(frozen=frozen, eq=eq)
+                    class C(base):
+                        i: int
+
+                # Now, make sure it hashes as expected.
+                if expected == 'unhashable':
+                    c = C(10)
+                    with self.assertRaisesRegex(TypeError, 'unhashable type'):
+                        hash(c)
+
+                elif expected == 'base':
+                    self.assertEqual(hash(C(10)), 301)
+
+                elif expected == 'object':
+                    # I'm not sure what test to use here.  object's
+                    #  hash isn't based on id(), so calling hash()
+                    #  won't tell us much.  So, just check the
+                    #  function used is object's.
+                    self.assertIs(C.__hash__, object.__hash__)
+
+                elif expected == 'tuple':
+                    self.assertEqual(hash(C(42)), hash((42,)))
+
+                else:
+                    assert False, f'unknown value for expected={expected!r}'
+
+
+class TestFrozen(unittest.TestCase):
+    def test_frozen(self):
+        @dataclass(frozen=True)
+        class C:
+            i: int
+
+        c = C(10)
+        self.assertEqual(c.i, 10)
+        with self.assertRaises(FrozenInstanceError):
+            c.i = 5
+        self.assertEqual(c.i, 10)
+
+    def test_frozen_empty(self):
+        @dataclass(frozen=True)
+        class C:
+            pass
+
+        c = C()
+        self.assertFalse(hasattr(c, 'i'))
+        with self.assertRaises(FrozenInstanceError):
+            c.i = 5
+        self.assertFalse(hasattr(c, 'i'))
+        with self.assertRaises(FrozenInstanceError):
+            del c.i
+
+    def test_inherit(self):
+        @dataclass(frozen=True)
+        class C:
+            i: int
+
+        @dataclass(frozen=True)
+        class D(C):
+            j: int
+
+        d = D(0, 10)
+        with self.assertRaises(FrozenInstanceError):
+            d.i = 5
+        with self.assertRaises(FrozenInstanceError):
+            d.j = 6
+        self.assertEqual(d.i, 0)
+        self.assertEqual(d.j, 10)
+
+    def test_inherit_nonfrozen_from_empty_frozen(self):
+        @dataclass(frozen=True)
+        class C:
+            pass
+
+        with self.assertRaisesRegex(TypeError,
+                                    'cannot inherit non-frozen dataclass from a frozen one'):
+            @dataclass
+            class D(C):
+                j: int
+
+    def test_inherit_nonfrozen_from_empty(self):
+        @dataclass
+        class C:
+            pass
+
+        @dataclass
+        class D(C):
+            j: int
+
+        d = D(3)
+        self.assertEqual(d.j, 3)
+        self.assertIsInstance(d, C)
+
+    # Test both ways: with an intermediate normal (non-dataclass)
+    #  class and without an intermediate class.
+    def test_inherit_nonfrozen_from_frozen(self):
+        for intermediate_class in [True, False]:
+            with self.subTest(intermediate_class=intermediate_class):
+                @dataclass(frozen=True)
+                class C:
+                    i: int
+
+                if intermediate_class:
+                    class I(C): pass
+                else:
+                    I = C
+
+                with self.assertRaisesRegex(TypeError,
+                                            'cannot inherit non-frozen dataclass from a frozen one'):
+                    @dataclass
+                    class D(I):
+                        pass
+
+    def test_inherit_frozen_from_nonfrozen(self):
+        for intermediate_class in [True, False]:
+            with self.subTest(intermediate_class=intermediate_class):
+                @dataclass
+                class C:
+                    i: int
+
+                if intermediate_class:
+                    class I(C): pass
+                else:
+                    I = C
+
+                with self.assertRaisesRegex(TypeError,
+                                            'cannot inherit frozen dataclass from a non-frozen one'):
+                    @dataclass(frozen=True)
+                    class D(I):
+                        pass
+
+    def test_inherit_from_normal_class(self):
+        for intermediate_class in [True, False]:
+            with self.subTest(intermediate_class=intermediate_class):
+                class C:
+                    pass
+
+                if intermediate_class:
+                    class I(C): pass
+                else:
+                    I = C
+
+                @dataclass(frozen=True)
+                class D(I):
+                    i: int
+
+            d = D(10)
+            with self.assertRaises(FrozenInstanceError):
+                d.i = 5
+
+    def test_non_frozen_normal_derived(self):
+        # See bpo-32953.
+
+        @dataclass(frozen=True)
+        class D:
+            x: int
+            y: int = 10
+
+        class S(D):
+            pass
+
+        s = S(3)
+        self.assertEqual(s.x, 3)
+        self.assertEqual(s.y, 10)
+        s.cached = True
+
+        # But can't change the frozen attributes.
+        with self.assertRaises(FrozenInstanceError):
+            s.x = 5
+        with self.assertRaises(FrozenInstanceError):
+            s.y = 5
+        self.assertEqual(s.x, 3)
+        self.assertEqual(s.y, 10)
+        self.assertEqual(s.cached, True)
+
+        with self.assertRaises(FrozenInstanceError):
+            del s.x
+        self.assertEqual(s.x, 3)
+        with self.assertRaises(FrozenInstanceError):
+            del s.y
+        self.assertEqual(s.y, 10)
+        del s.cached
+        self.assertFalse(hasattr(s, 'cached'))
+        with self.assertRaises(AttributeError) as cm:
+            del s.cached
+        self.assertNotIsInstance(cm.exception, FrozenInstanceError)
+
+    def test_non_frozen_normal_derived_from_empty_frozen(self):
+        @dataclass(frozen=True)
+        class D:
+            pass
+
+        class S(D):
+            pass
+
+        s = S()
+        self.assertFalse(hasattr(s, 'x'))
+        s.x = 5
+        self.assertEqual(s.x, 5)
+
+        del s.x
+        self.assertFalse(hasattr(s, 'x'))
+        with self.assertRaises(AttributeError) as cm:
+            del s.x
+        self.assertNotIsInstance(cm.exception, FrozenInstanceError)
+
+    def test_overwriting_frozen(self):
+        # frozen uses __setattr__ and __delattr__.
+        with self.assertRaisesRegex(TypeError,
+                                    'Cannot overwrite attribute __setattr__'):
+            @dataclass(frozen=True)
+            class C:
+                x: int
+                def __setattr__(self):
+                    pass
+
+        with self.assertRaisesRegex(TypeError,
+                                    'Cannot overwrite attribute __delattr__'):
+            @dataclass(frozen=True)
+            class C:
+                x: int
+                def __delattr__(self):
+                    pass
+
+        @dataclass(frozen=False)
+        class C:
+            x: int
+            def __setattr__(self, name, value):
+                self.__dict__['x'] = value * 2
+        self.assertEqual(C(10).x, 20)
+
+    def test_frozen_hash(self):
+        @dataclass(frozen=True)
+        class C:
+            x: Any
+
+        # If x is immutable, we can compute the hash.  No exception is
+        # raised.
+        hash(C(3))
+
+        # If x is mutable, computing the hash is an error.
+        with self.assertRaisesRegex(TypeError, 'unhashable type'):
+            hash(C({}))
+
+
+class TestSlots(unittest.TestCase):
+    def test_simple(self):
+        @dataclass
+        class C:
+            __slots__ = ('x',)
+            x: Any
+
+        # There was a bug where a variable in a slot was assumed to
+        #  also have a default value (of type
+        #  types.MemberDescriptorType).
+        with self.assertRaisesRegex(TypeError,
+                                    r"__init__\(\) missing 1 required positional argument: 'x'"):
+            C()
+
+        # We can create an instance, and assign to x.
+        c = C(10)
+        self.assertEqual(c.x, 10)
+        c.x = 5
+        self.assertEqual(c.x, 5)
+
+        # We can't assign to anything else.
+        with self.assertRaisesRegex(AttributeError, "'C' object has no attribute 'y'"):
+            c.y = 5
+
+    def test_derived_added_field(self):
+        # See bpo-33100.
+        @dataclass
+        class Base:
+            __slots__ = ('x',)
+            x: Any
+
+        @dataclass
+        class Derived(Base):
+            x: int
+            y: int
+
+        d = Derived(1, 2)
+        self.assertEqual((d.x, d.y), (1, 2))
+
+        # We can add a new field to the derived instance.
+        d.z = 10
+
+    def test_generated_slots(self):
+        @dataclass(slots=True)
+        class C:
+            x: int
+            y: int
+
+        c = C(1, 2)
+        self.assertEqual((c.x, c.y), (1, 2))
+
+        c.x = 3
+        c.y = 4
+        self.assertEqual((c.x, c.y), (3, 4))
+
+        with self.assertRaisesRegex(AttributeError, "'C' object has no attribute 'z'"):
+            c.z = 5
+
+    def test_add_slots_when_slots_exists(self):
+        with self.assertRaisesRegex(TypeError, '^C already specifies __slots__$'):
+            @dataclass(slots=True)
+            class C:
+                __slots__ = ('x',)
+                x: int
+
+    def test_generated_slots_value(self):
+
+        class Root:
+            __slots__ = {'x'}
+
+        class Root2(Root):
+            __slots__ = {'k': '...', 'j': ''}
+
+        class Root3(Root2):
+            __slots__ = ['h']
+
+        class Root4(Root3):
+            __slots__ = 'aa'
+
+        @dataclass(slots=True)
+        class Base(Root4):
+            y: int
+            j: str
+            h: str
+
+        self.assertEqual(Base.__slots__, ('y', ))
+
+        @dataclass(slots=True)
+        class Derived(Base):
+            aa: float
+            x: str
+            z: int
+            k: str
+            h: str
+
+        self.assertEqual(Derived.__slots__, ('z', ))
+
+        @dataclass
+        class AnotherDerived(Base):
+            z: int
+
+        self.assertNotIn('__slots__', AnotherDerived.__dict__)
+
+    def test_cant_inherit_from_iterator_slots(self):
+
+        class Root:
+            __slots__ = iter(['a'])
+
+        class Root2(Root):
+            __slots__ = ('b', )
+
+        with self.assertRaisesRegex(
+           TypeError,
+            "^Slots of 'Root' cannot be determined"
+        ):
+            @dataclass(slots=True)
+            class C(Root2):
+                x: int
+
+    def test_returns_new_class(self):
+        class A:
+            x: int
+
+        B = dataclass(A, slots=True)
+        self.assertIsNot(A, B)
+
+        self.assertFalse(hasattr(A, "__slots__"))
+        self.assertTrue(hasattr(B, "__slots__"))
+
+    # Can't be local to test_frozen_pickle.
+    @dataclass(frozen=True, slots=True)
+    class FrozenSlotsClass:
+        foo: str
+        bar: int
+
+    @dataclass(frozen=True)
+    class FrozenWithoutSlotsClass:
+        foo: str
+        bar: int
+
+    def test_frozen_pickle(self):
+        # bpo-43999
+
+        self.assertEqual(self.FrozenSlotsClass.__slots__, ("foo", "bar"))
+        for proto in range(pickle.HIGHEST_PROTOCOL + 1):
+            with self.subTest(proto=proto):
+                obj = self.FrozenSlotsClass("a", 1)
+                p = pickle.loads(pickle.dumps(obj, protocol=proto))
+                self.assertIsNot(obj, p)
+                self.assertEqual(obj, p)
+
+                obj = self.FrozenWithoutSlotsClass("a", 1)
+                p = pickle.loads(pickle.dumps(obj, protocol=proto))
+                self.assertIsNot(obj, p)
+                self.assertEqual(obj, p)
+
+    @dataclass(frozen=True, slots=True)
+    class FrozenSlotsGetStateClass:
+        foo: str
+        bar: int
+
+        getstate_called: bool = field(default=False, compare=False)
+
+        def __getstate__(self):
+            object.__setattr__(self, 'getstate_called', True)
+            return [self.foo, self.bar]
+
+    @dataclass(frozen=True, slots=True)
+    class FrozenSlotsSetStateClass:
+        foo: str
+        bar: int
+
+        setstate_called: bool = field(default=False, compare=False)
+
+        def __setstate__(self, state):
+            object.__setattr__(self, 'setstate_called', True)
+            object.__setattr__(self, 'foo', state[0])
+            object.__setattr__(self, 'bar', state[1])
+
+    @dataclass(frozen=True, slots=True)
+    class FrozenSlotsAllStateClass:
+        foo: str
+        bar: int
+
+        getstate_called: bool = field(default=False, compare=False)
+        setstate_called: bool = field(default=False, compare=False)
+
+        def __getstate__(self):
+            object.__setattr__(self, 'getstate_called', True)
+            return [self.foo, self.bar]
+
+        def __setstate__(self, state):
+            object.__setattr__(self, 'setstate_called', True)
+            object.__setattr__(self, 'foo', state[0])
+            object.__setattr__(self, 'bar', state[1])
+
+    def test_frozen_slots_pickle_custom_state(self):
+        for proto in range(pickle.HIGHEST_PROTOCOL + 1):
+            with self.subTest(proto=proto):
+                obj = self.FrozenSlotsGetStateClass('a', 1)
+                dumped = pickle.dumps(obj, protocol=proto)
+
+                self.assertTrue(obj.getstate_called)
+                self.assertEqual(obj, pickle.loads(dumped))
+
+        for proto in range(pickle.HIGHEST_PROTOCOL + 1):
+            with self.subTest(proto=proto):
+                obj = self.FrozenSlotsSetStateClass('a', 1)
+                obj2 = pickle.loads(pickle.dumps(obj, protocol=proto))
+
+                self.assertTrue(obj2.setstate_called)
+                self.assertEqual(obj, obj2)
+
+        for proto in range(pickle.HIGHEST_PROTOCOL + 1):
+            with self.subTest(proto=proto):
+                obj = self.FrozenSlotsAllStateClass('a', 1)
+                dumped = pickle.dumps(obj, protocol=proto)
+
+                self.assertTrue(obj.getstate_called)
+
+                obj2 = pickle.loads(dumped)
+                self.assertTrue(obj2.setstate_called)
+                self.assertEqual(obj, obj2)
+
+    def test_slots_with_default_no_init(self):
+        # Originally reported in bpo-44649.
+        @dataclass(slots=True)
+        class A:
+            a: str
+            b: str = field(default='b', init=False)
+
+        obj = A("a")
+        self.assertEqual(obj.a, 'a')
+        self.assertEqual(obj.b, 'b')
+
+    def test_slots_with_default_factory_no_init(self):
+        # Originally reported in bpo-44649.
+        @dataclass(slots=True)
+        class A:
+            a: str
+            b: str = field(default_factory=lambda:'b', init=False)
+
+        obj = A("a")
+        self.assertEqual(obj.a, 'a')
+        self.assertEqual(obj.b, 'b')
+
+    def test_slots_no_weakref(self):
+        @dataclass(slots=True)
+        class A:
+            # No weakref.
+            pass
+
+        self.assertNotIn("__weakref__", A.__slots__)
+        a = A()
+        with self.assertRaisesRegex(TypeError,
+                                    "cannot create weak reference"):
+            weakref.ref(a)
+        with self.assertRaises(AttributeError):
+            a.__weakref__
+
+    def test_slots_weakref(self):
+        @dataclass(slots=True, weakref_slot=True)
+        class A:
+            a: int
+
+        self.assertIn("__weakref__", A.__slots__)
+        a = A(1)
+        a_ref = weakref.ref(a)
+
+        self.assertIs(a.__weakref__, a_ref)
+
+    def test_slots_weakref_base_str(self):
+        class Base:
+            __slots__ = '__weakref__'
+
+        @dataclass(slots=True)
+        class A(Base):
+            a: int
+
+        # __weakref__ is in the base class, not A.  But an A is still weakref-able.
+        self.assertIn("__weakref__", Base.__slots__)
+        self.assertNotIn("__weakref__", A.__slots__)
+        a = A(1)
+        weakref.ref(a)
+
+    def test_slots_weakref_base_tuple(self):
+        # Same as test_slots_weakref_base, but use a tuple instead of a string
+        # in the base class.
+        class Base:
+            __slots__ = ('__weakref__',)
+
+        @dataclass(slots=True)
+        class A(Base):
+            a: int
+
+        # __weakref__ is in the base class, not A.  But an A is still
+        # weakref-able.
+        self.assertIn("__weakref__", Base.__slots__)
+        self.assertNotIn("__weakref__", A.__slots__)
+        a = A(1)
+        weakref.ref(a)
+
+    def test_weakref_slot_without_slot(self):
+        with self.assertRaisesRegex(TypeError,
+                                    "weakref_slot is True but slots is False"):
+            @dataclass(weakref_slot=True)
+            class A:
+                a: int
+
+    def test_weakref_slot_make_dataclass(self):
+        A = make_dataclass('A', [('a', int),], slots=True, weakref_slot=True)
+        self.assertIn("__weakref__", A.__slots__)
+        a = A(1)
+        weakref.ref(a)
+
+        # And make sure if raises if slots=True is not given.
+        with self.assertRaisesRegex(TypeError,
+                                    "weakref_slot is True but slots is False"):
+            B = make_dataclass('B', [('a', int),], weakref_slot=True)
+
+    def test_weakref_slot_subclass_weakref_slot(self):
+        @dataclass(slots=True, weakref_slot=True)
+        class Base:
+            field: int
+
+        # A *can* also specify weakref_slot=True if it wants to (gh-93521)
+        @dataclass(slots=True, weakref_slot=True)
+        class A(Base):
+            ...
+
+        # __weakref__ is in the base class, not A.  But an instance of A
+        # is still weakref-able.
+        self.assertIn("__weakref__", Base.__slots__)
+        self.assertNotIn("__weakref__", A.__slots__)
+        a = A(1)
+        a_ref = weakref.ref(a)
+        self.assertIs(a.__weakref__, a_ref)
+
+    def test_weakref_slot_subclass_no_weakref_slot(self):
+        @dataclass(slots=True, weakref_slot=True)
+        class Base:
+            field: int
+
+        @dataclass(slots=True)
+        class A(Base):
+            ...
+
+        # __weakref__ is in the base class, not A.  Even though A doesn't
+        # specify weakref_slot, it should still be weakref-able.
+        self.assertIn("__weakref__", Base.__slots__)
+        self.assertNotIn("__weakref__", A.__slots__)
+        a = A(1)
+        a_ref = weakref.ref(a)
+        self.assertIs(a.__weakref__, a_ref)
+
+    def test_weakref_slot_normal_base_weakref_slot(self):
+        class Base:
+            __slots__ = ('__weakref__',)
+
+        @dataclass(slots=True, weakref_slot=True)
+        class A(Base):
+            field: int
+
+        # __weakref__ is in the base class, not A.  But an instance of
+        # A is still weakref-able.
+        self.assertIn("__weakref__", Base.__slots__)
+        self.assertNotIn("__weakref__", A.__slots__)
+        a = A(1)
+        a_ref = weakref.ref(a)
+        self.assertIs(a.__weakref__, a_ref)
+
+
+class TestDescriptors(unittest.TestCase):
+    def test_set_name(self):
+        # See bpo-33141.
+
+        # Create a descriptor.
+        class D:
+            def __set_name__(self, owner, name):
+                self.name = name + 'x'
+            def __get__(self, instance, owner):
+                if instance is not None:
+                    return 1
+                return self
+
+        # This is the case of just normal descriptor behavior, no
+        #  dataclass code is involved in initializing the descriptor.
+        @dataclass
+        class C:
+            c: int=D()
+        self.assertEqual(C.c.name, 'cx')
+
+        # Now test with a default value and init=False, which is the
+        #  only time this is really meaningful.  If not using
+        #  init=False, then the descriptor will be overwritten, anyway.
+        @dataclass
+        class C:
+            c: int=field(default=D(), init=False)
+        self.assertEqual(C.c.name, 'cx')
+        self.assertEqual(C().c, 1)
+
+    def test_non_descriptor(self):
+        # PEP 487 says __set_name__ should work on non-descriptors.
+        # Create a descriptor.
+
+        class D:
+            def __set_name__(self, owner, name):
+                self.name = name + 'x'
+
+        @dataclass
+        class C:
+            c: int=field(default=D(), init=False)
+        self.assertEqual(C.c.name, 'cx')
+
+    def test_lookup_on_instance(self):
+        # See bpo-33175.
+        class D:
+            pass
+
+        d = D()
+        # Create an attribute on the instance, not type.
+        d.__set_name__ = Mock()
+
+        # Make sure d.__set_name__ is not called.
+        @dataclass
+        class C:
+            i: int=field(default=d, init=False)
+
+        self.assertEqual(d.__set_name__.call_count, 0)
+
+    def test_lookup_on_class(self):
+        # See bpo-33175.
+        class D:
+            pass
+        D.__set_name__ = Mock()
+
+        # Make sure D.__set_name__ is called.
+        @dataclass
+        class C:
+            i: int=field(default=D(), init=False)
+
+        self.assertEqual(D.__set_name__.call_count, 1)
+
+    def test_init_calls_set(self):
+        class D:
+            pass
+
+        D.__set__ = Mock()
+
+        @dataclass
+        class C:
+            i: D = D()
+
+        # Make sure D.__set__ is called.
+        D.__set__.reset_mock()
+        c = C(5)
+        self.assertEqual(D.__set__.call_count, 1)
+
+    def test_getting_field_calls_get(self):
+        class D:
+            pass
+
+        D.__set__ = Mock()
+        D.__get__ = Mock()
+
+        @dataclass
+        class C:
+            i: D = D()
+
+        c = C(5)
+
+        # Make sure D.__get__ is called.
+        D.__get__.reset_mock()
+        value = c.i
+        self.assertEqual(D.__get__.call_count, 1)
+
+    def test_setting_field_calls_set(self):
+        class D:
+            pass
+
+        D.__set__ = Mock()
+
+        @dataclass
+        class C:
+            i: D = D()
+
+        c = C(5)
+
+        # Make sure D.__set__ is called.
+        D.__set__.reset_mock()
+        c.i = 10
+        self.assertEqual(D.__set__.call_count, 1)
+
+    def test_setting_uninitialized_descriptor_field(self):
+        class D:
+            pass
+
+        D.__set__ = Mock()
+
+        @dataclass
+        class C:
+            i: D
+
+        # D.__set__ is not called because there's no D instance to call it on
+        D.__set__.reset_mock()
+        c = C(5)
+        self.assertEqual(D.__set__.call_count, 0)
+
+        # D.__set__ still isn't called after setting i to an instance of D
+        # because descriptors don't behave like that when stored as instance vars
+        c.i = D()
+        c.i = 5
+        self.assertEqual(D.__set__.call_count, 0)
+
+    def test_default_value(self):
+        class D:
+            def __get__(self, instance: Any, owner: object) -> int:
+                if instance is None:
+                    return 100
+
+                return instance._x
+
+            def __set__(self, instance: Any, value: int) -> None:
+                instance._x = value
+
+        @dataclass
+        class C:
+            i: D = D()
+
+        c = C()
+        self.assertEqual(c.i, 100)
+
+        c = C(5)
+        self.assertEqual(c.i, 5)
+
+    def test_no_default_value(self):
+        class D:
+            def __get__(self, instance: Any, owner: object) -> int:
+                if instance is None:
+                    raise AttributeError()
+
+                return instance._x
+
+            def __set__(self, instance: Any, value: int) -> None:
+                instance._x = value
+
+        @dataclass
+        class C:
+            i: D = D()
+
+        with self.assertRaisesRegex(TypeError, 'missing 1 required positional argument'):
+            c = C()
+
+class TestStringAnnotations(unittest.TestCase):
+    def test_classvar(self):
+        # Some expressions recognized as ClassVar really aren't.  But
+        #  if you're using string annotations, it's not an exact
+        #  science.
+        # These tests assume that both "import typing" and "from
+        # typing import *" have been run in this file.
+        for typestr in ('ClassVar[int]',
+                        'ClassVar [int]',
+                        ' ClassVar [int]',
+                        'ClassVar',
+                        ' ClassVar ',
+                        'typing.ClassVar[int]',
+                        'typing.ClassVar[str]',
+                        ' typing.ClassVar[str]',
+                        'typing .ClassVar[str]',
+                        'typing. ClassVar[str]',
+                        'typing.ClassVar [str]',
+                        'typing.ClassVar [ str]',
+
+                        # Not syntactically valid, but these will
+                        #  be treated as ClassVars.
+                        'typing.ClassVar.[int]',
+                        'typing.ClassVar+',
+                        ):
+            with self.subTest(typestr=typestr):
+                @dataclass
+                class C:
+                    x: typestr
+
+                # x is a ClassVar, so C() takes no args.
+                C()
+
+                # And it won't appear in the class's dict because it doesn't
+                # have a default.
+                self.assertNotIn('x', C.__dict__)
+
+    def test_isnt_classvar(self):
+        for typestr in ('CV',
+                        't.ClassVar',
+                        't.ClassVar[int]',
+                        'typing..ClassVar[int]',
+                        'Classvar',
+                        'Classvar[int]',
+                        'typing.ClassVarx[int]',
+                        'typong.ClassVar[int]',
+                        'dataclasses.ClassVar[int]',
+                        'typingxClassVar[str]',
+                        ):
+            with self.subTest(typestr=typestr):
+                @dataclass
+                class C:
+                    x: typestr
+
+                # x is not a ClassVar, so C() takes one arg.
+                self.assertEqual(C(10).x, 10)
+
+    def test_initvar(self):
+        # These tests assume that both "import dataclasses" and "from
+        #  dataclasses import *" have been run in this file.
+        for typestr in ('InitVar[int]',
+                        'InitVar [int]'
+                        ' InitVar [int]',
+                        'InitVar',
+                        ' InitVar ',
+                        'dataclasses.InitVar[int]',
+                        'dataclasses.InitVar[str]',
+                        ' dataclasses.InitVar[str]',
+                        'dataclasses .InitVar[str]',
+                        'dataclasses. InitVar[str]',
+                        'dataclasses.InitVar [str]',
+                        'dataclasses.InitVar [ str]',
+
+                        # Not syntactically valid, but these will
+                        #  be treated as InitVars.
+                        'dataclasses.InitVar.[int]',
+                        'dataclasses.InitVar+',
+                        ):
+            with self.subTest(typestr=typestr):
+                @dataclass
+                class C:
+                    x: typestr
+
+                # x is an InitVar, so doesn't create a member.
+                with self.assertRaisesRegex(AttributeError,
+                                            "object has no attribute 'x'"):
+                    C(1).x
+
+    def test_isnt_initvar(self):
+        for typestr in ('IV',
+                        'dc.InitVar',
+                        'xdataclasses.xInitVar',
+                        'typing.xInitVar[int]',
+                        ):
+            with self.subTest(typestr=typestr):
+                @dataclass
+                class C:
+                    x: typestr
+
+                # x is not an InitVar, so there will be a member x.
+                self.assertEqual(C(10).x, 10)
+
+    def test_classvar_module_level_import(self):
+        from test.test_dataclasses import dataclass_module_1
+        from test.test_dataclasses import dataclass_module_1_str
+        from test.test_dataclasses import dataclass_module_2
+        from test.test_dataclasses import dataclass_module_2_str
+
+        for m in (dataclass_module_1, dataclass_module_1_str,
+                  dataclass_module_2, dataclass_module_2_str,
+                  ):
+            with self.subTest(m=m):
+                # There's a difference in how the ClassVars are
+                # interpreted when using string annotations or
+                # not. See the imported modules for details.
+                if m.USING_STRINGS:
+                    c = m.CV(10)
+                else:
+                    c = m.CV()
+                self.assertEqual(c.cv0, 20)
+
+
+                # There's a difference in how the InitVars are
+                # interpreted when using string annotations or
+                # not. See the imported modules for details.
+                c = m.IV(0, 1, 2, 3, 4)
+
+                for field_name in ('iv0', 'iv1', 'iv2', 'iv3'):
+                    with self.subTest(field_name=field_name):
+                        with self.assertRaisesRegex(AttributeError, f"object has no attribute '{field_name}'"):
+                            # Since field_name is an InitVar, it's
+                            # not an instance field.
+                            getattr(c, field_name)
+
+                if m.USING_STRINGS:
+                    # iv4 is interpreted as a normal field.
+                    self.assertIn('not_iv4', c.__dict__)
+                    self.assertEqual(c.not_iv4, 4)
+                else:
+                    # iv4 is interpreted as an InitVar, so it
+                    # won't exist on the instance.
+                    self.assertNotIn('not_iv4', c.__dict__)
+
+    def test_text_annotations(self):
+        from test.test_dataclasses import dataclass_textanno
+
+        self.assertEqual(
+            get_type_hints(dataclass_textanno.Bar),
+            {'foo': dataclass_textanno.Foo})
+        self.assertEqual(
+            get_type_hints(dataclass_textanno.Bar.__init__),
+            {'foo': dataclass_textanno.Foo,
+             'return': type(None)})
+
+
+ByMakeDataClass = make_dataclass('ByMakeDataClass', [('x', int)])
+ManualModuleMakeDataClass = make_dataclass('ManualModuleMakeDataClass',
+                                           [('x', int)],
+                                           module=__name__)
+WrongNameMakeDataclass = make_dataclass('Wrong', [('x', int)])
+WrongModuleMakeDataclass = make_dataclass('WrongModuleMakeDataclass',
+                                          [('x', int)],
+                                          module='custom')
+
+class TestMakeDataclass(unittest.TestCase):
+    def test_simple(self):
+        C = make_dataclass('C',
+                           [('x', int),
+                            ('y', int, field(default=5))],
+                           namespace={'add_one': lambda self: self.x + 1})
+        c = C(10)
+        self.assertEqual((c.x, c.y), (10, 5))
+        self.assertEqual(c.add_one(), 11)
+
+
+    def test_no_mutate_namespace(self):
+        # Make sure a provided namespace isn't mutated.
+        ns = {}
+        C = make_dataclass('C',
+                           [('x', int),
+                            ('y', int, field(default=5))],
+                           namespace=ns)
+        self.assertEqual(ns, {})
+
+    def test_base(self):
+        class Base1:
+            pass
+        class Base2:
+            pass
+        C = make_dataclass('C',
+                           [('x', int)],
+                           bases=(Base1, Base2))
+        c = C(2)
+        self.assertIsInstance(c, C)
+        self.assertIsInstance(c, Base1)
+        self.assertIsInstance(c, Base2)
+
+    def test_base_dataclass(self):
+        @dataclass
+        class Base1:
+            x: int
+        class Base2:
+            pass
+        C = make_dataclass('C',
+                           [('y', int)],
+                           bases=(Base1, Base2))
+        with self.assertRaisesRegex(TypeError, 'required positional'):
+            c = C(2)
+        c = C(1, 2)
+        self.assertIsInstance(c, C)
+        self.assertIsInstance(c, Base1)
+        self.assertIsInstance(c, Base2)
+
+        self.assertEqual((c.x, c.y), (1, 2))
+
+    def test_init_var(self):
+        def post_init(self, y):
+            self.x *= y
+
+        C = make_dataclass('C',
+                           [('x', int),
+                            ('y', InitVar[int]),
+                            ],
+                           namespace={'__post_init__': post_init},
+                           )
+        c = C(2, 3)
+        self.assertEqual(vars(c), {'x': 6})
+        self.assertEqual(len(fields(c)), 1)
+
+    def test_class_var(self):
+        C = make_dataclass('C',
+                           [('x', int),
+                            ('y', ClassVar[int], 10),
+                            ('z', ClassVar[int], field(default=20)),
+                            ])
+        c = C(1)
+        self.assertEqual(vars(c), {'x': 1})
+        self.assertEqual(len(fields(c)), 1)
+        self.assertEqual(C.y, 10)
+        self.assertEqual(C.z, 20)
+
+    def test_other_params(self):
+        C = make_dataclass('C',
+                           [('x', int),
+                            ('y', ClassVar[int], 10),
+                            ('z', ClassVar[int], field(default=20)),
+                            ],
+                           init=False)
+        # Make sure we have a repr, but no init.
+        self.assertNotIn('__init__', vars(C))
+        self.assertIn('__repr__', vars(C))
+
+        # Make sure random other params don't work.
+        with self.assertRaisesRegex(TypeError, 'unexpected keyword argument'):
+            C = make_dataclass('C',
+                               [],
+                               xxinit=False)
+
+    def test_no_types(self):
+        C = make_dataclass('Point', ['x', 'y', 'z'])
+        c = C(1, 2, 3)
+        self.assertEqual(vars(c), {'x': 1, 'y': 2, 'z': 3})
+        self.assertEqual(C.__annotations__, {'x': 'typing.Any',
+                                             'y': 'typing.Any',
+                                             'z': 'typing.Any'})
+
+        C = make_dataclass('Point', ['x', ('y', int), 'z'])
+        c = C(1, 2, 3)
+        self.assertEqual(vars(c), {'x': 1, 'y': 2, 'z': 3})
+        self.assertEqual(C.__annotations__, {'x': 'typing.Any',
+                                             'y': int,
+                                             'z': 'typing.Any'})
+
+    def test_module_attr(self):
+        self.assertEqual(ByMakeDataClass.__module__, __name__)
+        self.assertEqual(ByMakeDataClass(1).__module__, __name__)
+        self.assertEqual(WrongModuleMakeDataclass.__module__, "custom")
+        Nested = make_dataclass('Nested', [])
+        self.assertEqual(Nested.__module__, __name__)
+        self.assertEqual(Nested().__module__, __name__)
+
+    def test_pickle_support(self):
+        for klass in [ByMakeDataClass, ManualModuleMakeDataClass]:
+            for proto in range(pickle.HIGHEST_PROTOCOL + 1):
+                with self.subTest(proto=proto):
+                    self.assertEqual(
+                        pickle.loads(pickle.dumps(klass, proto)),
+                        klass,
+                    )
+                    self.assertEqual(
+                        pickle.loads(pickle.dumps(klass(1), proto)),
+                        klass(1),
+                    )
+
+    def test_cannot_be_pickled(self):
+        for klass in [WrongNameMakeDataclass, WrongModuleMakeDataclass]:
+            for proto in range(pickle.HIGHEST_PROTOCOL + 1):
+                with self.subTest(proto=proto):
+                    with self.assertRaises(pickle.PickleError):
+                        pickle.dumps(klass, proto)
+                    with self.assertRaises(pickle.PickleError):
+                        pickle.dumps(klass(1), proto)
+
+    def test_invalid_type_specification(self):
+        for bad_field in [(),
+                          (1, 2, 3, 4),
+                          ]:
+            with self.subTest(bad_field=bad_field):
+                with self.assertRaisesRegex(TypeError, r'Invalid field: '):
+                    make_dataclass('C', ['a', bad_field])
+
+        # And test for things with no len().
+        for bad_field in [float,
+                          lambda x:x,
+                          ]:
+            with self.subTest(bad_field=bad_field):
+                with self.assertRaisesRegex(TypeError, r'has no len\(\)'):
+                    make_dataclass('C', ['a', bad_field])
+
+    def test_duplicate_field_names(self):
+        for field in ['a', 'ab']:
+            with self.subTest(field=field):
+                with self.assertRaisesRegex(TypeError, 'Field name duplicated'):
+                    make_dataclass('C', [field, 'a', field])
+
+    def test_keyword_field_names(self):
+        for field in ['for', 'async', 'await', 'as']:
+            with self.subTest(field=field):
+                with self.assertRaisesRegex(TypeError, 'must not be keywords'):
+                    make_dataclass('C', ['a', field])
+                with self.assertRaisesRegex(TypeError, 'must not be keywords'):
+                    make_dataclass('C', [field])
+                with self.assertRaisesRegex(TypeError, 'must not be keywords'):
+                    make_dataclass('C', [field, 'a'])
+
+    def test_non_identifier_field_names(self):
+        for field in ['()', 'x,y', '*', '2@3', '', 'little johnny tables']:
+            with self.subTest(field=field):
+                with self.assertRaisesRegex(TypeError, 'must be valid identifiers'):
+                    make_dataclass('C', ['a', field])
+                with self.assertRaisesRegex(TypeError, 'must be valid identifiers'):
+                    make_dataclass('C', [field])
+                with self.assertRaisesRegex(TypeError, 'must be valid identifiers'):
+                    make_dataclass('C', [field, 'a'])
+
+    def test_underscore_field_names(self):
+        # Unlike namedtuple, it's okay if dataclass field names have
+        # an underscore.
+        make_dataclass('C', ['_', '_a', 'a_a', 'a_'])
+
+    def test_funny_class_names_names(self):
+        # No reason to prevent weird class names, since
+        # types.new_class allows them.
+        for classname in ['()', 'x,y', '*', '2@3', '']:
+            with self.subTest(classname=classname):
+                C = make_dataclass(classname, ['a', 'b'])
+                self.assertEqual(C.__name__, classname)
+
+class TestReplace(unittest.TestCase):
+    def test(self):
+        @dataclass(frozen=True)
+        class C:
+            x: int
+            y: int
+
+        c = C(1, 2)
+        c1 = replace(c, x=3)
+        self.assertEqual(c1.x, 3)
+        self.assertEqual(c1.y, 2)
+
+    def test_frozen(self):
+        @dataclass(frozen=True)
+        class C:
+            x: int
+            y: int
+            z: int = field(init=False, default=10)
+            t: int = field(init=False, default=100)
+
+        c = C(1, 2)
+        c1 = replace(c, x=3)
+        self.assertEqual((c.x, c.y, c.z, c.t), (1, 2, 10, 100))
+        self.assertEqual((c1.x, c1.y, c1.z, c1.t), (3, 2, 10, 100))
+
+
+        with self.assertRaisesRegex(ValueError, 'init=False'):
+            replace(c, x=3, z=20, t=50)
+        with self.assertRaisesRegex(ValueError, 'init=False'):
+            replace(c, z=20)
+            replace(c, x=3, z=20, t=50)
+
+        # Make sure the result is still frozen.
+        with self.assertRaisesRegex(FrozenInstanceError, "cannot assign to field 'x'"):
+            c1.x = 3
+
+        # Make sure we can't replace an attribute that doesn't exist,
+        #  if we're also replacing one that does exist.  Test this
+        #  here, because setting attributes on frozen instances is
+        #  handled slightly differently from non-frozen ones.
+        with self.assertRaisesRegex(TypeError, r"__init__\(\) got an unexpected "
+                                             "keyword argument 'a'"):
+            c1 = replace(c, x=20, a=5)
+
+    def test_invalid_field_name(self):
+        @dataclass(frozen=True)
+        class C:
+            x: int
+            y: int
+
+        c = C(1, 2)
+        with self.assertRaisesRegex(TypeError, r"__init__\(\) got an unexpected "
+                                    "keyword argument 'z'"):
+            c1 = replace(c, z=3)
+
+    def test_invalid_object(self):
+        @dataclass(frozen=True)
+        class C:
+            x: int
+            y: int
+
+        with self.assertRaisesRegex(TypeError, 'dataclass instance'):
+            replace(C, x=3)
+
+        with self.assertRaisesRegex(TypeError, 'dataclass instance'):
+            replace(0, x=3)
+
+    def test_no_init(self):
+        @dataclass
+        class C:
+            x: int
+            y: int = field(init=False, default=10)
+
+        c = C(1)
+        c.y = 20
+
+        # Make sure y gets the default value.
+        c1 = replace(c, x=5)
+        self.assertEqual((c1.x, c1.y), (5, 10))
+
+        # Trying to replace y is an error.
+        with self.assertRaisesRegex(ValueError, 'init=False'):
+            replace(c, x=2, y=30)
+
+        with self.assertRaisesRegex(ValueError, 'init=False'):
+            replace(c, y=30)
+
+    def test_classvar(self):
+        @dataclass
+        class C:
+            x: int
+            y: ClassVar[int] = 1000
+
+        c = C(1)
+        d = C(2)
+
+        self.assertIs(c.y, d.y)
+        self.assertEqual(c.y, 1000)
+
+        # Trying to replace y is an error: can't replace ClassVars.
+        with self.assertRaisesRegex(TypeError, r"__init__\(\) got an "
+                                    "unexpected keyword argument 'y'"):
+            replace(c, y=30)
+
+        replace(c, x=5)
+
+    def test_initvar_is_specified(self):
+        @dataclass
+        class C:
+            x: int
+            y: InitVar[int]
+
+            def __post_init__(self, y):
+                self.x *= y
+
+        c = C(1, 10)
+        self.assertEqual(c.x, 10)
+        with self.assertRaisesRegex(ValueError, r"InitVar 'y' must be "
+                                    "specified with replace()"):
+            replace(c, x=3)
+        c = replace(c, x=3, y=5)
+        self.assertEqual(c.x, 15)
+
+    def test_initvar_with_default_value(self):
+        @dataclass
+        class C:
+            x: int
+            y: InitVar[int] = None
+            z: InitVar[int] = 42
+
+            def __post_init__(self, y, z):
+                if y is not None:
+                    self.x += y
+                if z is not None:
+                    self.x += z
+
+        c = C(x=1, y=10, z=1)
+        self.assertEqual(replace(c), C(x=12))
+        self.assertEqual(replace(c, y=4), C(x=12, y=4, z=42))
+        self.assertEqual(replace(c, y=4, z=1), C(x=12, y=4, z=1))
+
+    def test_recursive_repr(self):
+        @dataclass
+        class C:
+            f: "C"
+
+        c = C(None)
+        c.f = c
+        self.assertEqual(repr(c), "TestReplace.test_recursive_repr.<locals>.C(f=...)")
+
+    def test_recursive_repr_two_attrs(self):
+        @dataclass
+        class C:
+            f: "C"
+            g: "C"
+
+        c = C(None, None)
+        c.f = c
+        c.g = c
+        self.assertEqual(repr(c), "TestReplace.test_recursive_repr_two_attrs"
+                                  ".<locals>.C(f=..., g=...)")
+
+    def test_recursive_repr_indirection(self):
+        @dataclass
+        class C:
+            f: "D"
+
+        @dataclass
+        class D:
+            f: "C"
+
+        c = C(None)
+        d = D(None)
+        c.f = d
+        d.f = c
+        self.assertEqual(repr(c), "TestReplace.test_recursive_repr_indirection"
+                                  ".<locals>.C(f=TestReplace.test_recursive_repr_indirection"
+                                  ".<locals>.D(f=...))")
+
+    def test_recursive_repr_indirection_two(self):
+        @dataclass
+        class C:
+            f: "D"
+
+        @dataclass
+        class D:
+            f: "E"
+
+        @dataclass
+        class E:
+            f: "C"
+
+        c = C(None)
+        d = D(None)
+        e = E(None)
+        c.f = d
+        d.f = e
+        e.f = c
+        self.assertEqual(repr(c), "TestReplace.test_recursive_repr_indirection_two"
+                                  ".<locals>.C(f=TestReplace.test_recursive_repr_indirection_two"
+                                  ".<locals>.D(f=TestReplace.test_recursive_repr_indirection_two"
+                                  ".<locals>.E(f=...)))")
+
+    def test_recursive_repr_misc_attrs(self):
+        @dataclass
+        class C:
+            f: "C"
+            g: int
+
+        c = C(None, 1)
+        c.f = c
+        self.assertEqual(repr(c), "TestReplace.test_recursive_repr_misc_attrs"
+                                  ".<locals>.C(f=..., g=1)")
+
+    ## def test_initvar(self):
+    ##     @dataclass
+    ##     class C:
+    ##         x: int
+    ##         y: InitVar[int]
+
+    ##     c = C(1, 10)
+    ##     d = C(2, 20)
+
+    ##     # In our case, replacing an InitVar is a no-op
+    ##     self.assertEqual(c, replace(c, y=5))
+
+    ##     replace(c, x=5)
+
+class TestAbstract(unittest.TestCase):
+    def test_abc_implementation(self):
+        class Ordered(abc.ABC):
+            @abc.abstractmethod
+            def __lt__(self, other):
+                pass
+
+            @abc.abstractmethod
+            def __le__(self, other):
+                pass
+
+        @dataclass(order=True)
+        class Date(Ordered):
+            year: int
+            month: 'Month'
+            day: 'int'
+
+        self.assertFalse(inspect.isabstract(Date))
+        self.assertGreater(Date(2020,12,25), Date(2020,8,31))
+
+    def test_maintain_abc(self):
+        class A(abc.ABC):
+            @abc.abstractmethod
+            def foo(self):
+                pass
+
+        @dataclass
+        class Date(A):
+            year: int
+            month: 'Month'
+            day: 'int'
+
+        self.assertTrue(inspect.isabstract(Date))
+        msg = "class Date without an implementation for abstract method 'foo'"
+        self.assertRaisesRegex(TypeError, msg, Date)
+
+
+class TestMatchArgs(unittest.TestCase):
+    def test_match_args(self):
+        @dataclass
+        class C:
+            a: int
+        self.assertEqual(C(42).__match_args__, ('a',))
+
+    def test_explicit_match_args(self):
+        ma = ()
+        @dataclass
+        class C:
+            a: int
+            __match_args__ = ma
+        self.assertIs(C(42).__match_args__, ma)
+
+    def test_bpo_43764(self):
+        @dataclass(repr=False, eq=False, init=False)
+        class X:
+            a: int
+            b: int
+            c: int
+        self.assertEqual(X.__match_args__, ("a", "b", "c"))
+
+    def test_match_args_argument(self):
+        @dataclass(match_args=False)
+        class X:
+            a: int
+        self.assertNotIn('__match_args__', X.__dict__)
+
+        @dataclass(match_args=False)
+        class Y:
+            a: int
+            __match_args__ = ('b',)
+        self.assertEqual(Y.__match_args__, ('b',))
+
+        @dataclass(match_args=False)
+        class Z(Y):
+            z: int
+        self.assertEqual(Z.__match_args__, ('b',))
+
+        # Ensure parent dataclass __match_args__ is seen, if child class
+        # specifies match_args=False.
+        @dataclass
+        class A:
+            a: int
+            z: int
+        @dataclass(match_args=False)
+        class B(A):
+            b: int
+        self.assertEqual(B.__match_args__, ('a', 'z'))
+
+    def test_make_dataclasses(self):
+        C = make_dataclass('C', [('x', int), ('y', int)])
+        self.assertEqual(C.__match_args__, ('x', 'y'))
+
+        C = make_dataclass('C', [('x', int), ('y', int)], match_args=True)
+        self.assertEqual(C.__match_args__, ('x', 'y'))
+
+        C = make_dataclass('C', [('x', int), ('y', int)], match_args=False)
+        self.assertNotIn('__match__args__', C.__dict__)
+
+        C = make_dataclass('C', [('x', int), ('y', int)], namespace={'__match_args__': ('z',)})
+        self.assertEqual(C.__match_args__, ('z',))
+
+
+class TestKeywordArgs(unittest.TestCase):
+    def test_no_classvar_kwarg(self):
+        msg = 'field a is a ClassVar but specifies kw_only'
+        with self.assertRaisesRegex(TypeError, msg):
+            @dataclass
+            class A:
+                a: ClassVar[int] = field(kw_only=True)
+
+        with self.assertRaisesRegex(TypeError, msg):
+            @dataclass
+            class A:
+                a: ClassVar[int] = field(kw_only=False)
+
+        with self.assertRaisesRegex(TypeError, msg):
+            @dataclass(kw_only=True)
+            class A:
+                a: ClassVar[int] = field(kw_only=False)
+
+    def test_field_marked_as_kwonly(self):
+        #######################
+        # Using dataclass(kw_only=True)
+        @dataclass(kw_only=True)
+        class A:
+            a: int
+        self.assertTrue(fields(A)[0].kw_only)
+
+        @dataclass(kw_only=True)
+        class A:
+            a: int = field(kw_only=True)
+        self.assertTrue(fields(A)[0].kw_only)
+
+        @dataclass(kw_only=True)
+        class A:
+            a: int = field(kw_only=False)
+        self.assertFalse(fields(A)[0].kw_only)
+
+        #######################
+        # Using dataclass(kw_only=False)
+        @dataclass(kw_only=False)
+        class A:
+            a: int
+        self.assertFalse(fields(A)[0].kw_only)
+
+        @dataclass(kw_only=False)
+        class A:
+            a: int = field(kw_only=True)
+        self.assertTrue(fields(A)[0].kw_only)
+
+        @dataclass(kw_only=False)
+        class A:
+            a: int = field(kw_only=False)
+        self.assertFalse(fields(A)[0].kw_only)
+
+        #######################
+        # Not specifying dataclass(kw_only)
+        @dataclass
+        class A:
+            a: int
+        self.assertFalse(fields(A)[0].kw_only)
+
+        @dataclass
+        class A:
+            a: int = field(kw_only=True)
+        self.assertTrue(fields(A)[0].kw_only)
+
+        @dataclass
+        class A:
+            a: int = field(kw_only=False)
+        self.assertFalse(fields(A)[0].kw_only)
+
+    def test_match_args(self):
+        # kw fields don't show up in __match_args__.
+        @dataclass(kw_only=True)
+        class C:
+            a: int
+        self.assertEqual(C(a=42).__match_args__, ())
+
+        @dataclass
+        class C:
+            a: int
+            b: int = field(kw_only=True)
+        self.assertEqual(C(42, b=10).__match_args__, ('a',))
+
+    def test_KW_ONLY(self):
+        @dataclass
+        class A:
+            a: int
+            _: KW_ONLY
+            b: int
+            c: int
+        A(3, c=5, b=4)
+        msg = "takes 2 positional arguments but 4 were given"
+        with self.assertRaisesRegex(TypeError, msg):
+            A(3, 4, 5)
+
+
+        @dataclass(kw_only=True)
+        class B:
+            a: int
+            _: KW_ONLY
+            b: int
+            c: int
+        B(a=3, b=4, c=5)
+        msg = "takes 1 positional argument but 4 were given"
+        with self.assertRaisesRegex(TypeError, msg):
+            B(3, 4, 5)
+
+        # Explicitly make a field that follows KW_ONLY be non-keyword-only.
+        @dataclass
+        class C:
+            a: int
+            _: KW_ONLY
+            b: int
+            c: int = field(kw_only=False)
+        c = C(1, 2, b=3)
+        self.assertEqual(c.a, 1)
+        self.assertEqual(c.b, 3)
+        self.assertEqual(c.c, 2)
+        c = C(1, b=3, c=2)
+        self.assertEqual(c.a, 1)
+        self.assertEqual(c.b, 3)
+        self.assertEqual(c.c, 2)
+        c = C(1, b=3, c=2)
+        self.assertEqual(c.a, 1)
+        self.assertEqual(c.b, 3)
+        self.assertEqual(c.c, 2)
+        c = C(c=2, b=3, a=1)
+        self.assertEqual(c.a, 1)
+        self.assertEqual(c.b, 3)
+        self.assertEqual(c.c, 2)
+
+    def test_KW_ONLY_as_string(self):
+        @dataclass
+        class A:
+            a: int
+            _: 'dataclasses.KW_ONLY'
+            b: int
+            c: int
+        A(3, c=5, b=4)
+        msg = "takes 2 positional arguments but 4 were given"
+        with self.assertRaisesRegex(TypeError, msg):
+            A(3, 4, 5)
+
+    def test_KW_ONLY_twice(self):
+        msg = "'Y' is KW_ONLY, but KW_ONLY has already been specified"
+
+        with self.assertRaisesRegex(TypeError, msg):
+            @dataclass
+            class A:
+                a: int
+                X: KW_ONLY
+                Y: KW_ONLY
+                b: int
+                c: int
+
+        with self.assertRaisesRegex(TypeError, msg):
+            @dataclass
+            class A:
+                a: int
+                X: KW_ONLY
+                b: int
+                Y: KW_ONLY
+                c: int
+
+        with self.assertRaisesRegex(TypeError, msg):
+            @dataclass
+            class A:
+                a: int
+                X: KW_ONLY
+                b: int
+                c: int
+                Y: KW_ONLY
+
+        # But this usage is okay, since it's not using KW_ONLY.
+        @dataclass
+        class A:
+            a: int
+            _: KW_ONLY
+            b: int
+            c: int = field(kw_only=True)
+
+        # And if inheriting, it's okay.
+        @dataclass
+        class A:
+            a: int
+            _: KW_ONLY
+            b: int
+            c: int
+        @dataclass
+        class B(A):
+            _: KW_ONLY
+            d: int
+
+        # Make sure the error is raised in a derived class.
+        with self.assertRaisesRegex(TypeError, msg):
+            @dataclass
+            class A:
+                a: int
+                _: KW_ONLY
+                b: int
+                c: int
+            @dataclass
+            class B(A):
+                X: KW_ONLY
+                d: int
+                Y: KW_ONLY
+
+
+    def test_post_init(self):
+        @dataclass
+        class A:
+            a: int
+            _: KW_ONLY
+            b: InitVar[int]
+            c: int
+            d: InitVar[int]
+            def __post_init__(self, b, d):
+                raise CustomError(f'{b=} {d=}')
+        with self.assertRaisesRegex(CustomError, 'b=3 d=4'):
+            A(1, c=2, b=3, d=4)
+
+        @dataclass
+        class B:
+            a: int
+            _: KW_ONLY
+            b: InitVar[int]
+            c: int
+            d: InitVar[int]
+            def __post_init__(self, b, d):
+                self.a = b
+                self.c = d
+        b = B(1, c=2, b=3, d=4)
+        self.assertEqual(asdict(b), {'a': 3, 'c': 4})
+
+    def test_defaults(self):
+        # For kwargs, make sure we can have defaults after non-defaults.
+        @dataclass
+        class A:
+            a: int = 0
+            _: KW_ONLY
+            b: int
+            c: int = 1
+            d: int
+
+        a = A(d=4, b=3)
+        self.assertEqual(a.a, 0)
+        self.assertEqual(a.b, 3)
+        self.assertEqual(a.c, 1)
+        self.assertEqual(a.d, 4)
+
+        # Make sure we still check for non-kwarg non-defaults not following
+        # defaults.
+        err_regex = "non-default argument 'z' follows default argument 'a'"
+        with self.assertRaisesRegex(TypeError, err_regex):
+            @dataclass
+            class A:
+                a: int = 0
+                z: int
+                _: KW_ONLY
+                b: int
+                c: int = 1
+                d: int
+
+    def test_make_dataclass(self):
+        A = make_dataclass("A", ['a'], kw_only=True)
+        self.assertTrue(fields(A)[0].kw_only)
+
+        B = make_dataclass("B",
+                           ['a', ('b', int, field(kw_only=False))],
+                           kw_only=True)
+        self.assertTrue(fields(B)[0].kw_only)
+        self.assertFalse(fields(B)[1].kw_only)
+
+
+if __name__ == '__main__':
+    unittest.main()
diff --git a/Lib/test/test_dataclasses/dataclass_module_1.py b/Lib/test/test_dataclasses/dataclass_module_1.py
new file mode 100644
index 0000000..87a33f8
--- /dev/null
+++ b/Lib/test/test_dataclasses/dataclass_module_1.py
@@ -0,0 +1,32 @@
+#from __future__ import annotations
+USING_STRINGS = False
+
+# dataclass_module_1.py and dataclass_module_1_str.py are identical
+# except only the latter uses string annotations.
+
+import dataclasses
+import typing
+
+T_CV2 = typing.ClassVar[int]
+T_CV3 = typing.ClassVar
+
+T_IV2 = dataclasses.InitVar[int]
+T_IV3 = dataclasses.InitVar
+
+@dataclasses.dataclass
+class CV:
+    T_CV4 = typing.ClassVar
+    cv0: typing.ClassVar[int] = 20
+    cv1: typing.ClassVar = 30
+    cv2: T_CV2
+    cv3: T_CV3
+    not_cv4: T_CV4  # When using string annotations, this field is not recognized as a ClassVar.
+
+@dataclasses.dataclass
+class IV:
+    T_IV4 = dataclasses.InitVar
+    iv0: dataclasses.InitVar[int]
+    iv1: dataclasses.InitVar
+    iv2: T_IV2
+    iv3: T_IV3
+    not_iv4: T_IV4  # When using string annotations, this field is not recognized as an InitVar.
diff --git a/Lib/test/test_dataclasses/dataclass_module_1_str.py b/Lib/test/test_dataclasses/dataclass_module_1_str.py
new file mode 100644
index 0000000..6de490b
--- /dev/null
+++ b/Lib/test/test_dataclasses/dataclass_module_1_str.py
@@ -0,0 +1,32 @@
+from __future__ import annotations
+USING_STRINGS = True
+
+# dataclass_module_1.py and dataclass_module_1_str.py are identical
+# except only the latter uses string annotations.
+
+import dataclasses
+import typing
+
+T_CV2 = typing.ClassVar[int]
+T_CV3 = typing.ClassVar
+
+T_IV2 = dataclasses.InitVar[int]
+T_IV3 = dataclasses.InitVar
+
+@dataclasses.dataclass
+class CV:
+    T_CV4 = typing.ClassVar
+    cv0: typing.ClassVar[int] = 20
+    cv1: typing.ClassVar = 30
+    cv2: T_CV2
+    cv3: T_CV3
+    not_cv4: T_CV4  # When using string annotations, this field is not recognized as a ClassVar.
+
+@dataclasses.dataclass
+class IV:
+    T_IV4 = dataclasses.InitVar
+    iv0: dataclasses.InitVar[int]
+    iv1: dataclasses.InitVar
+    iv2: T_IV2
+    iv3: T_IV3
+    not_iv4: T_IV4  # When using string annotations, this field is not recognized as an InitVar.
diff --git a/Lib/test/test_dataclasses/dataclass_module_2.py b/Lib/test/test_dataclasses/dataclass_module_2.py
new file mode 100644
index 0000000..68fb733
--- /dev/null
+++ b/Lib/test/test_dataclasses/dataclass_module_2.py
@@ -0,0 +1,32 @@
+#from __future__ import annotations
+USING_STRINGS = False
+
+# dataclass_module_2.py and dataclass_module_2_str.py are identical
+# except only the latter uses string annotations.
+
+from dataclasses import dataclass, InitVar
+from typing import ClassVar
+
+T_CV2 = ClassVar[int]
+T_CV3 = ClassVar
+
+T_IV2 = InitVar[int]
+T_IV3 = InitVar
+
+@dataclass
+class CV:
+    T_CV4 = ClassVar
+    cv0: ClassVar[int] = 20
+    cv1: ClassVar = 30
+    cv2: T_CV2
+    cv3: T_CV3
+    not_cv4: T_CV4  # When using string annotations, this field is not recognized as a ClassVar.
+
+@dataclass
+class IV:
+    T_IV4 = InitVar
+    iv0: InitVar[int]
+    iv1: InitVar
+    iv2: T_IV2
+    iv3: T_IV3
+    not_iv4: T_IV4  # When using string annotations, this field is not recognized as an InitVar.
diff --git a/Lib/test/test_dataclasses/dataclass_module_2_str.py b/Lib/test/test_dataclasses/dataclass_module_2_str.py
new file mode 100644
index 0000000..b363d17
--- /dev/null
+++ b/Lib/test/test_dataclasses/dataclass_module_2_str.py
@@ -0,0 +1,32 @@
+from __future__ import annotations
+USING_STRINGS = True
+
+# dataclass_module_2.py and dataclass_module_2_str.py are identical
+# except only the latter uses string annotations.
+
+from dataclasses import dataclass, InitVar
+from typing import ClassVar
+
+T_CV2 = ClassVar[int]
+T_CV3 = ClassVar
+
+T_IV2 = InitVar[int]
+T_IV3 = InitVar
+
+@dataclass
+class CV:
+    T_CV4 = ClassVar
+    cv0: ClassVar[int] = 20
+    cv1: ClassVar = 30
+    cv2: T_CV2
+    cv3: T_CV3
+    not_cv4: T_CV4  # When using string annotations, this field is not recognized as a ClassVar.
+
+@dataclass
+class IV:
+    T_IV4 = InitVar
+    iv0: InitVar[int]
+    iv1: InitVar
+    iv2: T_IV2
+    iv3: T_IV3
+    not_iv4: T_IV4  # When using string annotations, this field is not recognized as an InitVar.
diff --git a/Lib/test/test_dataclasses/dataclass_textanno.py b/Lib/test/test_dataclasses/dataclass_textanno.py
new file mode 100644
index 0000000..3eb6c94
--- /dev/null
+++ b/Lib/test/test_dataclasses/dataclass_textanno.py
@@ -0,0 +1,12 @@
+from __future__ import annotations
+
+import dataclasses
+
+
+class Foo:
+    pass
+
+
+@dataclasses.dataclass
+class Bar:
+    foo: Foo