'If a specific interface is passed into
L{SSHProtocolChecker.registerChecker}, that interface should be
registered instead of what the checker specifies in
credentialIntefaces.'

def test_registerCheckerWithInterface(self):

    checker = checkers.SSHProtocolChecker()
    self.assertEqual(checker.credentialInterfaces, [])
    checker.registerChecker(checkers.SSHPublicKeyDatabase(), IUsernamePassword)
    self.assertEqual(checker.credentialInterfaces, [IUsernamePassword])
    self.assertIsInstance(checker.checkers[IUsernamePassword], checkers.SSHPublicKeyDatabase)
