Can’t `runCurrent` be used to advance the event loop in case of nested coroutines launched with `Unc...

# coroutines

[Patrick Steiger]

Can’t runCurrent be used to advance the event loop in case of nested coroutines launched with UnconfinedTestDispatcher?
Below code outputs 1 2 4 3 5

fun test() = runTest(UnconfinedTestDispatcher()) {
  println(1)
  launch {
    println(2)
    launch { println(3) }
    runCurrent()
    println(4)
  }
  println(5)
}

[Ky]

I thought we have no control over execution order with 'Unconfined'. Everything is executed eagerly?

[Patrick Steiger]

Except when there are nested coroutines, in order to prevent StackOverflowException
Same for Dispatchers.Main.immediate

[Patrick Steiger]

In which case it forms an event loop

[Patrick Steiger]

Seems we can’t control this event loop at all in tests.

[Ky]

So you would see your expected behavior if you ran this same code in application code inside 'Dispatchers.UNCONFINED'?

although those clock operations are only available in coroutines test package

[Patrick Steiger]

Same code would output the same outside tests, yes

[Ky]

So it seems there is no case where we control execution order when using an unconfined dispatcher in kotlin. If the behavior is no different between tests and app code

[Patrick Steiger]

It’s been some time and I don’t remember exactly in which context I wanted to manually advance the event loop in tests, but I think In the end I chose to run runTest in standard dispatcher and using CoroutineStart.UNDISPATCHED in real code

Real code does want to avoid dispatch

[Patrick Steiger]

Ok based on this I guess it’s considered a bug