Hi! I'm rather new to working with coroutines and ...

# coroutines

[momrak]

Hi! I'm rather new to working with coroutines and I have a question regarding testing them.

I have a service similar to this

fun handleDelete(extIds: List<String>) {
        val ids = someClient1.getInternalIds(extIds) // get deleteable IDs

        try {
            runBlocking(<http://Dispatchers.IO|Dispatchers.IO>) { // use IO dispatcher as someClient2 makes a call to some remote service. 
                ids.forEach{ launch { someClient2.deleteId(it) } }
            }
        } catch (e: Exception) {
            handleException(e)
        }
    }

and I want to test it. My team uses Mockito and not Mockk, if that makes any difference.

Maybe the test does not make sense, but as I am not very familiar with coroutines I want to test that these are run correctly in paralell and that they exit the runBlocking block after they're all done. So I was thinking of mocking the responses from someClient2 so that say i have extIds = listof("123", "456") and the calls take respectively 500ms and 750ms, I want to check that in total this function does not use much more time than ~750ms and not (500+750)=1250ms.

Is this possible using Mockito? And is it actually a useful test? 🤔

[octylFractal]

https://kotlin.github.io/kotlinx.coroutines/kotlinx-coroutines-test/#testing-launch-or-async-with-delay may be of use

[momrak]

Yeah, I saw this, but not sure how to use it in this scenario. All examples I see use a suspending function where they call delay, but how can I relate that to my function being a remote call? Also Mockito has a ResponseWithDelay or smth class, but that delay does not play nice with the timings in runBlockingTest it seems like

[momrak]

So thats why I am wondering if the test is actually a stupid one, as I am struggling to find a solution for this. Am I basically just testing that the coroutines work as Jetbrains say they do..? Or is what I am trying to achieve not possible using Mockito, and testing coroutines should be done using Mockk?

[octylFractal]

well, if you want to time it, this isn't really a suspend function, so it's actually out of coroutines land

[octylFractal]

just use your test executors assertTimeout or similar

[octylFractal]

realistically, your code isn't properly structured to time well

[octylFractal]

well, actually, it's runBlocking, so that should actually work out fine

[octylFractal]

but there's no way to do anything with the coroutines inside the method, they're not exposed in any way

[octylFractal]

https://junit.org/junit5/docs/5.5.0/api/org/junit/jupiter/api/Assertions.html#assertTimeoutPreemptively(java.time.Duration,org.junit.jupiter.api.function.Executable) is likely what you want

[momrak]

Hmm, I could do as Jetbrains call it extract function refactoring and extract whats inside the launch into a suspending fcn, but yeah, then it is still only one function, and the paralell execution I want to test needs also the forEach to work, so that might not be a good idea anyway.

Cool, I'll check that out now!