Add support for testing pebble services interaction

[ghislainbourgeois]

There is currently no way in ops-scenario to test a charm interaction with a pebble service, like restarting it for example: self._container.restart(self._service_name).

The only way to accomplish this is to mock ops.model.Container.restart.

It would be nice to have a better way to do this, maybe as an automatic mock in the output state?

...

state_out = self.ctx.run(container.pebble_ready_event, state_in)

assert state_out.containers[0].services["ausf"].restarted

[PietroPasotti]

I'm hesitant to patch extra names into Container.services because at the moment scenario is using 'native' ops.pebble data structures internally, (Plan, ServiceInfo, etc...) so it'd be unexpected to have a different api in different contexts, when the objects are the same.
We could add something to Container:

assert state_out.containers[0].restarted('ausf')
assert state_out.containers[0].replanned
assert state_out.containers[0].sent_signals == ((9, "ausf", "foo"), ("SIGKILL", "bar-server"))

@benhoyt WDYT?

[PietroPasotti]

PS in light of #37, probably this kind of container-facing output mocks should end up in scenario.outputs as they are not quite persisted in the state.
Much like juju-log and action results.

[PietroPasotti]

@tonyandrewmeyer perhaps now we're using our own data structures instead of importing them from ops, this becomes more easy to implement in a clean way?
will draft something on top of v7 as soon as we release it

[dimaqq]

You're thinking that the library would offer a ready mock that mirrors the live API, and has some recording functionality. Is that right?

[tonyandrewmeyer]

Moved to canonical/operator#1427