def test_signDataWithAgent(self):
        """
        When connected to an agent, L{SSHUserAuthClient} can use it to
        request signatures of particular data with a particular L{Key}.
        """
        client = SSHUserAuthClient(b"user", ConchOptions(), None)
        agent = SSHAgentClient()
        transport = StringTransport()
        agent.makeConnection(transport)
        client.keyAgent = agent
        cleartext = b"Sign here"
        client.signData(self.rsaPublic, cleartext)
        self.assertEqual(
            transport.value(),
            b"\x00\x00\x01\x2d\r\x00\x00\x01\x17" + self.rsaPublic.blob() +
            b"\x00\x00\x00\t" + cleartext +
            b"\x00\x00\x00\x00")

        When connected to an agent, L{SSHUserAuthClient} can use it to
        request signatures of particular data with a particular L{Key}.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/conch/test/test_default.py