def test_roundtripEmptyAncillary(self):
        """
        L{send1msg} treats an empty ancillary data list the same way it treats
        receiving no argument for the ancillary parameter at all.
        """
        send1msg(self.input.fileno(), "hello, world!", 0, [])

        result = recv1msg(fd=self.output.fileno())
        self.assertEqual(result, ("hello, world!", 0, []))

        L{send1msg} treats an empty ancillary data list the same way it treats
        receiving no argument for the ancillary parameter at all.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/python/test/test_sendmsg.py