gh-124176: Add special support for dataclasses to `create_autospec` (#124429)

1 files changed, 16 insertions, 6 deletions

diff --git a/Lib/unittest/mock.py b/Lib/unittest/mock.py
index df3901f..21ca061 100644
--- a/Lib/unittest/mock.py
+++ b/Lib/unittest/mock.py
@@ -34,6 +34,7 @@ import builtins
 import pkgutil
 from inspect import iscoroutinefunction
 import threading
+from dataclasses import fields, is_dataclass
 from types import CodeType, ModuleType, MethodType
 from unittest.util import safe_repr
 from functools import wraps, partial
@@ -2756,7 +2757,15 @@ def create_autospec(spec, spec_set=False, instance=False, _parent=None,
         raise InvalidSpecError(f'Cannot autospec a Mock object. '
                                f'[object={spec!r}]')
     is_async_func = _is_async_func(spec)
-    _kwargs = {'spec': spec}
+
+    entries = [(entry, _missing) for entry in dir(spec)]
+    if is_type and instance and is_dataclass(spec):
+        dataclass_fields = fields(spec)
+        entries.extend((f.name, f.type) for f in dataclass_fields)
+        _kwargs = {'spec': [f.name for f in dataclass_fields]}
+    else:
+        _kwargs = {'spec': spec}
+
     if spec_set:
         _kwargs = {'spec_set': spec}
     elif spec is None:
@@ -2813,7 +2822,7 @@ def create_autospec(spec, spec_set=False, instance=False, _parent=None,
                                             _name='()', _parent=mock,
                                             wraps=wrapped)
 
-    for entry in dir(spec):
+    for entry, original in entries:
         if _is_magic(entry):
             # MagicMock already does the useful magic methods for us
             continue
@@ -2827,10 +2836,11 @@ def create_autospec(spec, spec_set=False, instance=False, _parent=None,
         # AttributeError on being fetched?
         # we could be resilient against it, or catch and propagate the
         # exception when the attribute is fetched from the mock
-        try:
-            original = getattr(spec, entry)
-        except AttributeError:
-            continue
+        if original is _missing:
+            try:
+                original = getattr(spec, entry)
+            except AttributeError:
+                continue
 
         child_kwargs = {'spec': original}
         # Wrap child attributes also.