def test_isChecker(self):
        """
        Verifies that strcred.makeChecker('anonymous') returns an object
        that implements the L{ICredentialsChecker} interface.
        """
        checker = strcred.makeChecker('anonymous')
        self.assertTrue(checkers.ICredentialsChecker.providedBy(checker))
        self.assertIn(credentials.IAnonymous, checker.credentialInterfaces)

        Verifies that strcred.makeChecker('anonymous') returns an object
        that implements the L{ICredentialsChecker} interface.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/cred/test/test_strcred.py