Issue #21271: Adds new keyword only parameters in reset_mock call

We now have two keyword only parameters in the reset_mock function to
selectively reset the return_value or the side_effects, or both.

Lib/unittest/mock.py

@@ -523,7 +523,7 @@ class NonCallableMock(Base):
     side_effect = property(__get_side_effect, __set_side_effect)
 
 
-    def reset_mock(self, visited=None):
+    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 = []
@@ -538,6 +538,11 @@ class NonCallableMock(Base):
         self.call_args_list = _CallList()
         self.method_calls = _CallList()
 
+        if return_value:
+            self._mock_return_value = DEFAULT
+        if side_effect:
+            self._mock_side_effect = None
+
         for child in self._mock_children.values():
             if isinstance(child, _SpecState):
                 continue

Lib/unittest/test/testmock/testmock.py

@@ -1277,6 +1277,24 @@ class MockTest(unittest.TestCase):
         self.assertEqual(m.method_calls[0], c)
         self.assertEqual(m.method_calls[1], i)
 
+    def test_reset_return_sideeffect(self):
+        m = Mock(return_value=10, side_effect=[2,3])
+        m.reset_mock(return_value=True, side_effect=True)
+        self.assertIsInstance(m.return_value, Mock)
+        self.assertEqual(m.side_effect, None)
+
+    def test_reset_return(self):
+        m = Mock(return_value=10, side_effect=[2,3])
+        m.reset_mock(return_value=True)
+        self.assertIsInstance(m.return_value, Mock)
+        self.assertNotEqual(m.side_effect, None)
+
+    def test_reset_sideeffect(self):
+        m = Mock(return_value=10, side_effect=[2,3])
+        m.reset_mock(side_effect=True)
+        self.assertEqual(m.return_value, 10)
+        self.assertEqual(m.side_effect, None)
+
     def test_mock_add_spec(self):
         class _One(object):
             one = 1