pythongh-124176: create_autospec must not change how dataclass defa…

…ults are mocked

Lib/test/test_unittest/testmock/testhelpers.py

@@ -1107,6 +1107,21 @@ class WithNonFields:
  with self.assertRaisesRegex(AttributeError, msg):
  mock.b
 
+ def test_dataclass_with_wider_default(self):
+ # If field defines an actual default, we don't need to change
+ # the default type. Since this is how it used to work before #124176
+ @dataclass
+ class WithWiderDefault:
+ narrow_default: int | None = field(default=30)
+
+ for mock in [
+ create_autospec(WithWiderDefault, instance=True),
+ create_autospec(WithWiderDefault()),
+ ]:
+ with self.subTest(mock=mock):
+ self.assertIs(mock.narrow_default.__class__, int)
+
+
 class TestCallList(unittest.TestCase):
 
  def test_args_list_contains_call_list(self):

Lib/unittest/mock.py

@@ -2758,13 +2758,15 @@ def create_autospec(spec, spec_set=False, instance=False, _parent=None,
  f'[object={spec!r}]')
  is_async_func = _is_async_func(spec)
 
- entries = [(entry, _missing) for entry in dir(spec)]
+ base_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)
+ entries = {f.name: f.type for f in dataclass_fields}
+ entries.update(base_entries)
  _kwargs = {'spec': [f.name for f in dataclass_fields]}
  else:
  _kwargs = {'spec': spec}
+ entries = base_entries
 
  if spec_set:
  _kwargs = {'spec_set': spec}
@@ -2822,7 +2824,7 @@ def create_autospec(spec, spec_set=False, instance=False, _parent=None,
  _name='()', _parent=mock,
  wraps=wrapped)
 
- for entry, original in entries:
+ for entry, original in entries.items():
  if _is_magic(entry):
  # MagicMock already does the useful magic methods for us
  continue