def test_defaultServers(self):
        """
        If no servers are given, addresses are taken from the file given by the
        I{resolvconf} parameter to L{client.createResolver}.
        """
        resolvconf = self.path()
        resolvconf.setContent(b"nameserver 127.1.2.3\n")
        with AlternateReactor(Clock()):
            resolver = client.createResolver(resolvconf=resolvconf.path)
        res = [r for r in resolver.resolvers if isinstance(r, client.Resolver)]
        self.assertEqual(1, len(res))
        self.assertEqual([], res[0].servers)
        self.assertEqual([("127.1.2.3", 53)], res[0].dynServers)

        If no servers are given, addresses are taken from the file given by the
        I{resolvconf} parameter to L{client.createResolver}.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/names/test/test_client.py