twisted: test my service's stop sequence

Question

We have a complex multiservice that needs to do some fairly intricate accounting when shutting down in order to implement a "graceful" shutdown.

I'm trying to write tests for this under trial. The issue is that the reactor is effectively a process-global resource, and shutting down my service means that trial's reactor is also stopped, which (of course) makes it explode.

This is documented to be a no-no in trial, but I need some kind of workaround that allows me to write my tests. My first thought was to use a mock.Mock, but this means we're not really using a reactor that's shutting down, which isn't going to give me behavior that's faithful to the actual shutdown process.

I believe what I need is a way to separate trial's reactor from the reactor of my service-under-test. Sharing a mutable resource between the test system and the system under test is surely an anti-pattern.

Answer 1

There's a difference between shutting down a service and stopping a reactor. You should be able to test most of the desired behavior with myservice.stopService. To test the code that actually initiates the shutdown, just mock out reactor.stop with self.patch(reactor, 'stop', mock.Mock()), and later assert that it was called. If you want to link the two, then have your mock stop call your service's stopService.