def test_cache(self):
        """
        L{client.createResolver} returns a L{resolve.ResolverChain} including a
        L{cache.CacheResolver}.
        """
        with AlternateReactor(Clock()):
            resolver = client.createResolver()
        res = [r for r in resolver.resolvers if isinstance(r, cache.CacheResolver)]
        self.assertEqual(1, len(res))

        L{client.createResolver} returns a L{resolve.ResolverChain} including a
        L{cache.CacheResolver}.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/names/test/test_client.py