def test_ipv6Resolver(self):
        """
        If the resolver is ipv6, open a ipv6 port.
        """

        fake = test_util.MemoryReactor()
        resolver = client.Resolver(servers=[('::1', 53)],
                                   reactor=fake)
        resolver.query(dns.Query(b'foo.example.com'))
        [(proto, transport)] = fake.udpPorts.items()
        interface = transport.getHost().host
        self.assertEqual("::", interface)

        If the resolver is ipv6, open a ipv6 port.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/names/test/test_client.py