I'm trying to test a function with a `delay()`. By...

# kotest

[Marcin Wisniowski]

I'm trying to test a function with a delay(). By using coroutineTestScope = true, Kotest is correctly skipping the delay and I can test the output. However, I also want to test that it delays for the correct amount of time. How can I check how much virtual time has elapsed? I thought testCoroutineScheduler.currentTime would tell me, but it returns 0.

[Adam S]

You can use testTimeSource()

https://github.com/kotest/kotest/blob/a19274d3259ba0f347f1f4749864f2b5d6fa26a6/kotest-common/src/commonMain/kotlin/io/kotest/common/testTimeSource.kt#L16

[Adam S]

oh, it's marked as internal 🤔

[Sam]

A more hands-off approach would just be to use delay() in your test itself. E.g.

delay(expectedDuration - 1)
assert(thing.isNotDone)
delay(1)
assert(thing.isDone)

[Marcin Wisniowski]

I don't want my test to actually take a long time to run, because of the delay

[Sam]

It won't—delays in the test are skipped by the scheduler, just the same as delays in the code under test

[Marcin Wisniowski]

Hmm, that could work then. I would presumably have to launch a separate coroutine to run my function, so I can concurrently do these delayed assertions?

[Sam]

That could work, yes. Maybe an async coroutine, and then you can use its Deferred result to check whether it's finished.