Respect mock spec when checking for unsafe prefixes

Lib/test/test_unittest/testmock/testmock.py

@@ -1655,6 +1655,18 @@ def test_mock_unsafe(self):
         m.assrt_foo_call()
         m.called_once_with()
 
+    def test_mock_safe_with_spec(self):
+        class Foo(object):
+            def called_frobnicate(self):
+                pass
+
+        m = Mock(spec=Foo)
+        m.called_frobnicate()
+
+        msg = "is not a valid assertion. Use a spec for the mock"
+        with self.assertRaisesRegex(AttributeError, msg):
+            m.called_frognicate()
+
     #Issue21262
     def test_assert_not_called(self):
         m = Mock()

Lib/unittest/mock.py

@@ -652,7 +652,7 @@ def __getattr__(self, name):
                 raise AttributeError("Mock object has no attribute %r" % name)
         elif _is_magic(name):
             raise AttributeError(name)
-        if not self._mock_unsafe:
+        if not self._mock_unsafe and name not in self._mock_methods:
             if name.startswith(('assert', 'assret', 'asert', 'aseert', 'assrt', 'called_')):
                 raise AttributeError(
                     f"{name!r} is not a valid assertion. Use a spec "