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

        result = recvmsg(self.output)
        self.assertEqual(result, (b"hello, world!", [], 0))

        L{sendmsg} 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