def test_mailExchangeRecord(self):
        """
        The DNS client can issue an MX query and receive a response including
        an MX record as well as any A record hints.
        """
        return self.namesTest(
            self.resolver.lookupMailExchange(b"test-domain.com"),
            [dns.Record_MX(10, b"host.test-domain.com", ttl=19283784),
             dns.Record_A(b"123.242.1.5", ttl=19283784),
             dns.Record_A(b"0.255.0.255", ttl=19283784)])

        The DNS client can issue an MX query and receive a response including
        an MX record as well as any A record hints.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/names/test/test_names.py