def _resolvConfTest(self, resolver, filename):
        """
        Verify that C{resolver} has a L{client.Resolver} with a configuration
        filename set to C{filename}.
        """
        res = [r for r in resolver.resolvers if isinstance(r, client.Resolver)]
        self.assertEqual(1, len(res))
        self.assertEqual(res[0].resolv, filename)

        Verify that C{resolver} has a L{client.Resolver} with a configuration
        filename set to C{filename}.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/names/test/test_client.py