def test_becomesResolver(self):
        """
        The L{root.DeferredResolver} initially returned by L{root.bootstrap}
        becomes a L{root.Resolver} when the supplied resolver has successfully
        looked up all root hints.
        """
        stubResolver = StubResolver()
        deferredResolver = root.bootstrap(stubResolver)
        for d in stubResolver.pendingResults:
            d.callback('192.0.2.101')
        self.assertIsInstance(deferredResolver, Resolver)

        The L{root.DeferredResolver} initially returned by L{root.bootstrap}
        becomes a L{root.Resolver} when the supplied resolver has successfully
        looked up all root hints.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/names/test/test_rootresolve.py