Reliably testing code that adopts Swift Concurrency?

[Joe_Groff]

@filiplazov

I don't think that the underlying problem are the system APIs like Notification Center but we have no tooling to progress time reliably to assert that state changes between bodies of async work. If we do not control it we are always going to have flakey tests where we have to depend on the system scheduler and hope we assert at the correct time.

I don't think that's necessarily true. If you substitute "Tasks" for "threads", and made a similar statement: "if we don't have control of the hardware to reliably progress CPU instructions in a certain way, we are always going to have flaky tests", then that hopefully rings false at first blush. It is possible to build testable concurrent systems out of hardware threads using synchronization, without changing the scheduling environment, and it ought to ultimately be possible with Swift concurrency as well, with the right tools.