<https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-test/> mentions the possibility to...

# coroutines

[CLOVIS]

https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-test/ mentions the possibility to create multiple StandardTestDispatcher in a single test. Why would you want to do this?

[Sam]

In the example in the docs, it seems like the only real reason is to give the two dispatchers different names, for debugging purposes

[Sam]

I guess I can also imagine a scenario where the code under test has some logic like

if (currentDispatcher == dispatcher1) {
  doOneThing()
} else {
  doSomeOtherThing()
}

[Sam]

So the identity of the dispatcher might sometimes be important

[CLOVIS]

Where is the event loop implemented? Will that allow both dispatchers to start tasks in parallel? (AFAIK runTest is single-threaded?)

[Sam]

The dispatcher is mostly just a wrapper around the TestCoroutineScheduler, which is what contains the event loop. The runTest function just grabs the scheduler from the TestScope and runs its event loop.

[Sam]

So you wouldn't be able to use two different schedulers, unless you were manually advancing the event loop somehow. As far as I understand it, the scheduler has to be wired up to the runTest function for it to actually start running anything.

[CLOVIS]

Ah, I see. I always confuse schedulers and dispatchers

[Sam]

I think the distinction is only really made for test dispatchers. Elsewhere in the coroutines library, dispatcher and scheduler seem to be mostly synonymous.