[3.12] gh-123934: Fix MagicMock not to reset magic method return values (GH-124038)

Lib/test/test_unittest/testmock/testmagicmethods.py

@@ -331,6 +331,45 @@ def test_magic_methods_fspath(self):
  self.assertEqual(os.fspath(mock), expected_path)
  mock.__fspath__.assert_called_once()
 
+ def test_magic_mock_does_not_reset_magic_returns(self):
+ # https://github.com/python/cpython/issues/123934
+ for reset in (True, False):
+ with self.subTest(reset=reset):
+ mm = MagicMock()
+ self.assertIs(type(mm.__str__()), str)
+ mm.__str__.assert_called_once()
+
+ self.assertIs(type(mm.__hash__()), int)
+ mm.__hash__.assert_called_once()
+
+ for _ in range(3):
+ # Repeat reset several times to be sure:
+ mm.reset_mock(return_value=reset)
+
+ self.assertIs(type(mm.__str__()), str)
+ mm.__str__.assert_called_once()
+
+ self.assertIs(type(mm.__hash__()), int)
+ mm.__hash__.assert_called_once()
+
+ def test_magic_mock_resets_manual_mocks(self):
+ mm = MagicMock()
+ mm.__iter__ = MagicMock(return_value=iter([1]))
+ mm.custom = MagicMock(return_value=2)
+ self.assertEqual(list(iter(mm)), [1])
+ self.assertEqual(mm.custom(), 2)
+
+ mm.reset_mock(return_value=True)
+ self.assertEqual(list(iter(mm)), [])
+ self.assertIsInstance(mm.custom(), MagicMock)
+
+ def test_magic_mock_resets_manual_mocks_empty_iter(self):
+ mm = MagicMock()
+ mm.__iter__.return_value = []
+ self.assertEqual(list(iter(mm)), [])
+
+ mm.reset_mock(return_value=True)
+ self.assertEqual(list(iter(mm)), [])
 
  def test_magic_methods_and_spec(self):
  class Iterable(object):

Lib/unittest/mock.py

@@ -598,7 +598,7 @@ def __set_side_effect(self, value):
  side_effect = property(__get_side_effect, __set_side_effect)
 
 
- def reset_mock(self,  visited=None,*, return_value=False, side_effect=False):
+ def reset_mock(self, visited=None, *, return_value=False, side_effect=False):
  "Restore the mock object to its initial state."
  if visited is None:
  visited = []
@@ -2189,6 +2189,17 @@ def mock_add_spec(self, spec, spec_set=False):
  self._mock_add_spec(spec, spec_set)
  self._mock_set_magics()
 
+ def reset_mock(self, /, *args, return_value=False, **kwargs):
+ if (
+ return_value
+ and self._mock_name
+ and _is_magic(self._mock_name)
+ ):
+ # Don't reset return values for magic methods,
+ # otherwise `m.__str__` will start
+ # to return `MagicMock` instances, instead of `str` instances.
+ return_value = False
+ super().reset_mock(*args, return_value=return_value, **kwargs)
 
 
 class MagicProxy(Base):

Misc/NEWS.d/next/Library/2024-09-13-10-34-19.gh-issue-123934.yMe7mL.rst

@@ -0,0 +1,2 @@
+Fix :class:`unittest.mock.MagicMock` reseting magic methods return values
+after ``.reset_mock(return_value=True)`` was called.