I want it in 6.x branch too

That would be for 6.2, but I’d like to better understand the use case to see if there isn’t a better solution.

@fabpot In tests, I run worker and later want to check sent messages.

I use this trait - worker is runned with messenger.listener.reset_services subscriber. I need this to test all flow, as some of my code depends on service resetting.

I don't understand what's missing with the existing testing infrastructure based the profiler.
Since the class is not final, you can achieve this on your side.
For Symfony, I'm not convinced this makes sense.