'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}.'

def test_checkPassword(self):

    c = CramMD5Credentials()
    chal = c.getChallenge()
    c.response = hexlify(HMAC('secret', chal).digest())
    self.assertTrue(c.checkPassword('secret'))
