Are there any good examples available yet using new Kotlinx Coroutines 1.6 `runtTest` in `commonTest...

# multiplatform

[John O'Reilly]

Are there any good examples available yet using new Kotlinx Coroutines 1.6 runtTest in commonTest tests? I have a basic test that tests flow which works if run for Android or JVM but for iOS target I'm getting following.

UncompletedCoroutinesError: After waiting for 60000 ms, the test coroutine is not completing

[Martin Rajniak]

I was also looking for a good example without success.

But if it helps these tests work with Coroutines 1.6 with runTest in commonTest for iOS
https://github.com/MartinRajniak/CatViewerDemo/blob/main/shared/src/commonTest/kotlin/eu/rajniak/cat/CatsTest.kt

[Martin Rajniak]

I only found runTest docs
https://kotlin.github.io/kotlinx.coroutines/kotlinx-coroutines-test/kotlinx.coroutines.test/run-test.html
that don't mention case when dispatcher is injected in production code (and should be replaced in tests).

[John O'Reilly]

Thanks, will take a look at that

[Martin Rajniak]

I started using kotlinx-coroutines-test again after I read that in Coroutines 1.6 they added

• kotlinx-coroutines-test with the new reworked API and multiplatform support

Switched in this commit
https://github.com/MartinRajniak/CatViewerDemo/commit/5f6ba59489f306515ed59a719f30e0fbc04bf9ff#diff-7907192102e6f5b21406[…]c38ca72dbd8f450bca381e762

[Martin Rajniak]

Here they talk more about the new API
https://blog.jetbrains.com/kotlin/2021/12/introducing-kotlinx-coroutines-1-6-0/#kotlinx-coroutines-test-update

and migration
https://github.com/Kotlin/kotlinx.coroutines/blob/master/kotlinx-coroutines-test/MIGRATION.md

most interesting for me was Migration to runTest

[John O'Reilly]

fwiw this is the test I'm trying to run....I'm suspecting I might need to add some specific dispatcher related plumbing for it to work for iOS

https://github.com/joreilly/StarWars/blob/main/shared/src/commonTest/kotlin/dev/johnoreilly/starwars/shared/StarWarsRepositoryTest.kt

[Martin Rajniak]

Isn't it only coincidence that it failed on iOS?

I mean if it was a race condition then the fact that it failed on specific platform would not be a clue 🙂

(then again you probably tried it multiple times)

According to my understanding, this exception occurs when you are using a different dispatcher

https://stackoverflow.com/questions/61224047/unit-testing-coroutines-runblockingtest-this-job-has-not-completed-yet/67897542#67897542

In StarWarsRepository you are using
withContext(Dispatchers.Default)

I would assume you have to replace that with TestScope in tests (see the quote before).

Now that runTest works properly with asynchronous completions, runBlocking is only occasionally useful. As is, most uses of runBlocking in tests come from the need to interact with dispatchers that execute on other threads, like <http://Dispatchers.IO|Dispatchers.IO> or Dispatchers.Default.

https://github.com/Kotlin/kotlinx.coroutines/blob/master/kotlinx-coroutines-test/MIGRATION.md#replace-runblocking-with-runtest

Injecting dispatcher worked for me. The main point is to make sure you are using the same test dispatcher instance in the block inside runBlockingTest { }.

https://github.com/Kotlin/kotlinx.coroutines/issues/1204#issuecomment-857354670

[Martin Rajniak]

For example, here they talk about how to do it to support skipping delays when withContext is used
https://github.com/Kotlin/kotlinx.coroutines/tree/master/kotlinx-coroutines-test#virtual-time-support-with-other-dispatchers

[John O'Reilly]

I actually switched over in that repo after that to use an Apollo specific runTest and working ok now....needed seemingly due to particular thread switcing that Apollo is doing right now

[John O'Reilly]

Needed in particular when using Kotlin/Native

[Martin Rajniak]

glad to hear that you figured it out 🙂

I thought that some external dependency might be causing issues

I read somewhere in the documentation that they discuss what to do if you can't inject scope because it is used in external dependency

I can't remember what is the proposed solution, but I would assume that:
• either library plays along (like you mention with Apollo),
• or library only uses suspend functions and client handles dispatchers,

[John O'Reilly]

I think also that move to new memory model will also potentially simplify some of these interactions

[Martin Rajniak]

true - might be another variable 🤯

I am already using new memory model with coroutines 1.6

[John O'Reilly]

btw re. the withContext code, that isn't coming in to play in this particular test but agreed that should probably inject dispatcher for that