def test_caches(self):
        """
        L{server.DNSServerFactory.__init__} accepts a C{caches} argument. The
        value of this argument is a list and is used to extend the C{resolver}
        L{resolve.ResolverChain}.
        """
        dummyResolver = object()
        self.assertEqual(
            server.DNSServerFactory(
                caches=[dummyResolver]).resolver.resolvers,
            [dummyResolver])

        L{server.DNSServerFactory.__init__} accepts a C{caches} argument. The
        value of this argument is a list and is used to extend the C{resolver}
        L{resolve.ResolverChain}.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/names/test/test_server.py