def test_checkPassword(self):
        """
        When a valid response (which is a hex digest of the challenge that has
        been encrypted by the user's shared secret) is set on the
        L{CramMD5Credentials} that created the challenge, and C{checkPassword}
        is called with the user's shared secret, it will return L{True}.
        """
        c = CramMD5Credentials()
        chal = c.getChallenge()
        c.response = hexlify(HMAC(b'secret', chal).digest())
        self.assertTrue(c.checkPassword(b'secret'))

        When a valid response (which is a hex digest of the challenge that has
        been encrypted by the user's shared secret) is set on the
        L{CramMD5Credentials} that created the challenge, and C{checkPassword}
        is called with the user's shared secret, it will return L{True}.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/cred/test/test_cramauth.py