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# coroutines

[Slackbot]

This message was deleted.

[jw]

You need to inject the clock into that function via a parameter and then use the virtual time clock in your test.

[janvladimirmostert]

context(Clock)
	suspend inline fun <T> slowdown(duration: Duration, block: () -> T): T {
		var result: T
		val timeTaken = [e-mail] {
			result = block()
		}
		delay(duration - timeTaken)
		return result
	}

then in runTest scope, I should use currentTime and in normal runBlocking scope, `System.currentTimeInMilliSeconds`before and after block ...

I guess that'll work

Thanks Jake!

[ephemient]

unrelated, but you could

val (result, timeTaken) = measureTimedValue { ... }

[ephemient]

I'd use a TimeSource instead of Clock, defaulting to Monotonic, but either way you do have to provide the test value yourself since there isn't a public way of extracting it from the coroutine context

[hfhbd]

There is a timeSource: https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-test/kotlinx.coroutines.test/test-time-source.html

[hfhbd]

So you could use runTest { testTimeSource.measureTimedValue {} }

[ephemient]

yes, but the slowdown function can't pull that out of its context - the test still has to pass it along

[hfhbd]

Okay that's true. But the testTimeSource supports delay-skipping.

[ephemient]

yep, that's basically what I was recommending

[ephemient]

for this case in particular,

suspend fun <T> slowdown(duration: Duration, block: () -> T): T = coroutineScope {
    launch { delay(duration) }
    block()
}

would achieve the same result without having to deal with time, but in general you do need to use the test timesource or create a fake clock based on test time in order to work with test delay skipping