def test_wrappedOnPersistentReturned(self):
        """
        If L{client.HTTPConnectionPool.getConnection} returns a previously
        cached connection, it will get wrapped in a
        L{client._RetryingHTTP11ClientProtocol}.
        """
        pool = client.HTTPConnectionPool(Clock())

        # Add a connection to the cache:
        protocol = StubHTTPProtocol()
        protocol.makeConnection(StringTransport())
        pool._putConnection(123, protocol)

        # Retrieve it, it should come back wrapped in a
        # _RetryingHTTP11ClientProtocol:
        d = pool.getConnection(123, DummyEndpoint())

        def gotConnection(connection):
            self.assertIsInstance(connection,
                                  client._RetryingHTTP11ClientProtocol)
            self.assertIdentical(connection._clientProtocol, protocol)
        return d.addCallback(gotConnection)

        If L{client.HTTPConnectionPool.getConnection} returns a previously
        cached connection, it will get wrapped in a
        L{client._RetryingHTTP11ClientProtocol}.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/web/test/test_agent.py