twisted: test my service's stop sequence

twisted: test my service's stop sequence

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.