def test_mx(self):
        """
        Two L{dns.Record_MX} instances compare equal if and only if they have
        the same preference, name, and ttl.
        """
        # Vary the preference
        self._equalityTest(
            dns.Record_MX(10, b'example.org', 20),
            dns.Record_MX(10, b'example.org', 20),
            dns.Record_MX(100, b'example.org', 20))
        # Vary the name
        self._equalityTest(
            dns.Record_MX(10, b'example.org', 20),
            dns.Record_MX(10, b'example.org', 20),
            dns.Record_MX(10, b'example.net', 20))
        # Vary the ttl
        self._equalityTest(
            dns.Record_MX(10, b'example.org', 20),
            dns.Record_MX(10, b'example.org', 20),
            dns.Record_MX(10, b'example.org', 200))

        Two L{dns.Record_MX} instances compare equal if and only if they have
        the same preference, name, and ttl.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/names/test/test_dns.py