def test_cancelGetConnectionCancelsEndpointConnect(self):
        """
        Cancelling the C{Deferred} returned from
        L{HTTPConnectionPool.getConnection} cancels the C{Deferred} returned
        by opening a new connection with the given endpoint.
        """
        self.assertEqual(self.pool._connections, {})
        connectionResult = Deferred()

        class Endpoint:
            def connect(self, factory):
                return connectionResult

        d = self.pool.getConnection(12345, Endpoint())
        d.cancel()
        self.assertEqual(self.failureResultOf(connectionResult).type,
                         CancelledError)

        Cancelling the C{Deferred} returned from
        L{HTTPConnectionPool.getConnection} cancels the C{Deferred} returned
        by opening a new connection with the given endpoint.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/web/test/test_agent.py