gh-100739: Respect mock spec when checking for unsafe prefixes (GH-100740)

(cherry picked from commit 7f1eefc6f4)

Co-authored-by: Christian Klein <167265+cklein@users.noreply.github.com>
Co-authored-by: Nikita Sobolev <mail@sobolevn.me>

Lib/unittest/mock.py

@@ -647,7 +647,7 @@ class NonCallableMock(Base):
                 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 (not self._mock_methods or name not in self._mock_methods):
             if name.startswith(('assert', 'assret', 'asert', 'aseert', 'assrt')):
                 raise AttributeError(
                     f"{name!r} is not a valid assertion. Use a spec "

Lib/unittest/test/testmock/testmock.py

@@ -1652,6 +1652,22 @@ class MockTest(unittest.TestCase):
         m.aseert_foo_call()
         m.assrt_foo_call()
 
+    # gh-100739
+    def test_mock_safe_with_spec(self):
+        class Foo(object):
+            def assert_bar(self):
+                pass
+
+            def assertSome(self):
+                pass
+
+        m = Mock(spec=Foo)
+        m.assert_bar()
+        m.assertSome()
+
+        m.assert_bar.assert_called_once()
+        m.assertSome.assert_called_once()
+
     #Issue21262
     def test_assert_not_called(self):
         m = Mock()

Misc/NEWS.d/next/Library/2023-01-04-09-53-38.gh-issue-100740.-j5UjI.rst

@@ -0,0 +1 @@
+Fix ``unittest.mock.Mock`` not respecting the spec for attribute names prefixed with ``assert``.