def test_getPublicKeyAgentFallback(self):
        """
        If an agent is present, but doesn't return a key,
        L{SSHUserAuthClient.getPublicKey} continue with the normal key lookup.
        """
        options = ConchOptions()
        options.identitys = [self.rsaFile.path]
        agent = SSHAgentClient()
        client = SSHUserAuthClient(b"user",  options, None)
        client.keyAgent = agent
        key = client.getPublicKey()
        self.assertTrue(key.isPublic())
        self.assertEqual(key, self.rsaPublic)

        If an agent is present, but doesn't return a key,
        L{SSHUserAuthClient.getPublicKey} continue with the normal key lookup.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/conch/test/test_default.py