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Hi, im trying to write some tests around some code that delays before taking an action.
however, delays are skipped when using `runTest` and its making testing the timeout impossible.
am i missing something? im trying to use `advanceTimeBy` to maneuver around this delay for tests but it seems useless as the delays are just skipped

What is the timeout for? How does the system behave differently depending on whether the timeout finished or not?

and the timeout completes if a flow doesn't emit in that time window

``` fun &lt;T: Any&gt; Flow&lt;T&gt;.ifDelayed(timeMillis: Long, block: () -&gt; Unit): Flow&lt;T&gt; = channelFlow {
     val delayJob = launch {
         delay(timeMillis)
         block()
     }
 
     collect {
         delayJob.cancelAndJoin()
         send(it)
     }
 }```

may not be correct, found an answer on stackoverflow that I'm still working to adapt and understand, and testing it properly is a part of that process

How I would do it:

```@Test
fun lambdaIsNotCalledIfTimeoutDidntEnd() = runTest {
    var called = false
    flow {
        delay(100)
        emit(Unit)
    }.ifDelayed(1000) {
        called = true
    }.collect()
    assertFalse(called)
}

@Test
fun lambdaIsCalledIfTimeoutEnds() = runTest {
    var called = false
    flow {
        delay(5000)
        emit(Unit)
    }.ifDelayed(1000) {
        called = true
    }.collect()
    assertTrue(called)
}```

the thing for me here is understanding advanceTimeBy is useless for testing delays

It's not useless, it's just that what you want to test is whether the lambda is called or not. You don't really care about the control of time at all

In general, I recommend testing the _effect_ of things rather than the things themselves. It's called black box testing, if you want to read more about it

&gt; You don’t really care about the control of time at all
I think in many cases you actually do! So, I would agree that `advanceTimeBy` doesn’t appear to be very helpful in situations like this. I’ve noticed a common sentiment among developers, including myself, who are confused about what `advanceTimeBy` is supposed to do and how to use it.

This thread alone… <https://kotlinlang.slack.com/archives/C1CFAFJSK/p1677339643532769>