'Test receiving an empty challenge message.'

def test_onChallengeEmpty(self):

    d = self.init.start()
    challenge = domish.Element((NS_XMPP_SASL, 'challenge'))
    self.init.onChallenge(challenge)
    self.assertEqual('', self.init.mechanism.challenge)
    self.init.onSuccess(None)
    return d
