Hi! I don’t understand why this Coroutine test wi...

# coroutines

[Christophe Dongieux]

Hi!

I don’t understand why this Coroutine test with delays fails, do you have any idea?

@Test
fun `Foobar is foo`() = runTest {
    val job = launch {
        println("Coroutine 1: Going to sleep for 3000. currentTime = $currentTime")
        delay(3000)
        println("Coroutine 1: Delay is over. currentTime = $currentTime")
    }
    launch {
        println("Coroutine 2: Going to sleep for 1000. currentTime = $currentTime")
        delay(1000)
        println("Coroutine 2: Delay is over, cancelling other Coroutine. currentTime = $currentTime")
        job.cancel()
    }
    advanceTimeBy(500)
    println("advance 500: currentTime 1 = $currentTime")

    advanceTimeBy(500)
    println("advance 500: currentTime 2 = $currentTime")

    advanceUntilIdle()
    println("advanceUntilIdle: currentTime 3 = $currentTime")

    assertEquals(1000, currentTime)
}

The output is:

Coroutine 1: Going to sleep for 3000. currentTime = 0
Coroutine 2: Going to sleep for 1000. currentTime = 0
advance 500: currentTime 1 = 500
advance 500: currentTime 2 = 1000
Coroutine 2: Delay is over, cancelling other Coroutine. currentTime = 1000
advanceUntilIdle: currentTime 3 = 3000

expected:<1000> but was:<3000>
Expected :1000
Actual   :3000

As Coroutine 1 is canceled I don’t understand why currentTime 3 is 3000 instead of 1000.

[mkrussel]

The call to advanceUntilIdle will advance the clock until all the current delays are completed, including the one for 3000 in the first launch.

[Christophe Dongieux]

Yeah but it is cancelled after 1000. So it should be idle sooner than 3000, right?

[mkrussel]

I've found in many cases just advancing the time doesn't make the coroutine wake up from delay, but instead I need to do runCurrent (not sure the name) after I do the advanceTime call.

[Christophe Dongieux]

According to the output I pasted Coroutine 2 wakes up after its delay(1000).
And I can see Coroutine 1 is cancelled if I put a try/catch block around its delay(3000).

[mkrussel]

Might be a bug in the advanceUntilIdle function where it is still waiting for canceled delays.

[Christophe Dongieux]

It seems someone reported the same problem here: https://kotlinlang.slack.com/archives/C1CFAFJSK/p1636822119273500