def test_requestAvatarIdInvalidCredential(self):
        """
        If the passed credentials aren't handled by any registered checker,
        L{SSHProtocolChecker} should raise L{UnhandledCredentials}.
        """
        checker = checkers.SSHProtocolChecker()
        d = checker.requestAvatarId(UsernamePassword(b'test', b'test'))
        return self.assertFailure(d, UnhandledCredentials)

        If the passed credentials aren't handled by any registered checker,
        L{SSHProtocolChecker} should raise L{UnhandledCredentials}.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/conch/test/test_checkers.py