def test_flags(self):
        """
        The C{flags} argument to L{recv1msg} is passed on to the underlying
        C{recvmsg} call, to affect it in whatever way is defined by those
        flags.
        """
        # See test_flags in SendmsgTests
        reader, writer = socketpair(AF_UNIX)
        exc = self.assertRaises(
            error, recv1msg, reader.fileno(), MSG_DONTWAIT)
        self.assertEqual(exc.args[0], errno.EAGAIN)

        The C{flags} argument to L{recv1msg} is passed on to the underlying
        C{recvmsg} call, to affect it in whatever way is defined by those
        flags.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/python/test/test_sendmsg.py