def test_failOnAddingUnsupportedChecker(self):
        """
        When addChecker is called with a checker that does not implement any
        supported interfaces, it fails.
        """
        options = OptionsForUsernameHashedPassword()
        self.assertRaises(strcred.UnsupportedInterfaces,
                          options.addChecker, self.badChecker)

        When addChecker is called with a checker that does not implement any
        supported interfaces, it fails.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/cred/test/test_strcred.py