bpo-31177: Skip deleted attributes while calling reset_mock (GH-9302)

(cherry picked from commit edeca92c84)

Co-authored-by: Xtreak <tirkarthi@users.noreply.github.com>

Lib/unittest/mock.py

@@ -541,7 +541,7 @@ class NonCallableMock(Base):
             self._mock_side_effect = None
 
         for child in self._mock_children.values():
-            if isinstance(child, _SpecState):
+            if isinstance(child, _SpecState) or child is _deleted:
                 continue
             child.reset_mock(visited)
 

Lib/unittest/test/testmock/testmock.py

@@ -1566,6 +1566,16 @@ class MockTest(unittest.TestCase):
             self.assertRaises(AttributeError, getattr, mock, 'f')
 
 
+    def test_reset_mock_does_not_raise_on_attr_deletion(self):
+        # bpo-31177: reset_mock should not raise AttributeError when attributes
+        # were deleted in a mock instance
+        mock = Mock()
+        mock.child = True
+        del mock.child
+        mock.reset_mock()
+        self.assertFalse(hasattr(mock, 'child'))
+
+
     def test_class_assignable(self):
         for mock in Mock(), MagicMock():
             self.assertNotIsInstance(mock, int)

Misc/NEWS.d/next/Library/2018-09-14-10-38-18.bpo-31177.Sv91TN.rst

@@ -0,0 +1,2 @@
+Fix bug that prevented using :meth:`reset_mock <unittest.mock.Mock.reset_mock>`
+on mock instances with deleted attributes