1 files changed, 77 insertions, 0 deletions
diff --git a/Lib/test/test_dataclasses.py b/Lib/test/test_dataclasses.py
index 16ee4c7..8e645ae 100644
--- a/Lib/test/test_dataclasses.py
+++ b/Lib/test/test_dataclasses.py
@@ -3699,6 +3699,83 @@ class TestKeywordArgs(unittest.TestCase):
         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: