How do I test the following ``` Test fun distributedTest2 =

Question

How do I test the following ``` Test fun distributedTest2 = runTest repeat 1000 val state updates = MergeableValue Bar Instant fromEpochMilliseconds 0 distribute state is mutablestateflow updates is mutablesharedflow that also updates state val otherSource = uuid updates emit DistributedMergeable Update otherSource MergeableValue Baz Instant fromEpochMilliseconds 1 updates emit DistributedMergeable Update otherSource MergeableValue Bat Instant fromEpochMilliseconds 2 What do do here to make sure I can assert `state` assertEquals Bat state value value ``` Basically I have a MutableStateFlow `state` and a MutableSharedFlow `updates` By emitting into `updates` I update among other stuff also the `state` However for the life of me I can not see how to test this In an application this works as expected Basically this is the `distribute ` function ```data class DistributedMergeable lt T Mergeable lt T gt gt val states MutableStateFlow lt T gt val updates MutableSharedFlow lt Update lt T gt gt data class Update lt T Mergeable lt T gt gt val source UUID val value T fun lt T Mergeable lt T gt gt T distribute updates MutableSharedFlow lt DistributedMergeable Update lt T gt gt scope CoroutineScope = CoroutineScope EmptyCoroutineContext DistributedMergeable lt T gt val source = uuid val states = MutableStateFlow this states onEach newState gt println $newState updates emit DistributedMergeable Update source newState launchIn scope updates onEach update gt if update source == source println Same source $update return onEach if update value == states value println Same state $update return onEach val merged = states value merge update value println Merged $update gt $merged states value = merged launchIn scope return DistributedMergeable states updates ```

Joffrey · Answer

Why repeat 1000 times the same test Your test should instead be made deterministic by injecting the test dispatcher from `runTest` don t repeat and rely on chance and likelyhood

Nick Allen · Answer

To answer the commented question If you want to wait for all the coroutines to finish their work use `TestScope runCurrent`

Joffrey · Answer

It is often wrong to initialize a scope like this as a default argument Doing this prevents you from cancelling this scope The caller of `distribute ` should provide the scope or the function should be suspend otherwise you break structured concurrency unless you create some sort of closeable object that holds a reference to the scope which is not the case here

Joffrey · Answer

If you pass the scope that you get from `runTest` to `distribute ` you ll be able to make use of the test dispatcher s facilities like < Nick Allen> is mentioning here In particular `advanceUntilIdle` would be useful to you here

Nick Allen · Answer

You `waitUntil` in the earlier deleted post s thread That is using the test clock which always just advances immediately and because of a bug in your logic it exits normally instead of throwing The code you are trying to test is using a real dispatcher completely unrelated to the TestScope using other threads So it s just a race condition on whether the predicate check loop or the tested code finishes first Like < Joffrey> said pass the test scope in

Arjan van Wieringen · Answer

Thanks for the replies I ll pas the test scope in then < Joffrey> I am repeating 1000 times because I was seeing non deterministic behavior and as such this is why I was opening this thread I still keep stumbling over the basic coroutine issues it seems

Arjan van Wieringen · Answer

Okay I ve got it working now I ve exposed the Job as well so I can cancel it in order to stop the indefinite suspending of the hot flows ``` Test fun distributedTest2 = runTest val state updates job = MergeableValue Bar Instant fromEpochMilliseconds 0 distribute this val otherSource = uuid runCurrent launch updates emit DistributedMergeable Update otherSource MergeableValue Baz Instant fromEpochMilliseconds 1 updates emit DistributedMergeable Update otherSource MergeableValue Bat Instant fromEpochMilliseconds 2 runCurrent assertEquals Bat state value value job cancel ``` The only issue I have so far is the fact that I need to run `runCurrent` at the top Otherwise the updates aren t received which is I think because the Job launching those collectors hasn t been running yet ``` fun lt T Mergeable lt T gt gt T distribute updates MutableSharedFlow lt DistributedMergeable Update lt T gt gt scope CoroutineScope DistributedMergeable lt T gt val source = uuid val states = MutableStateFlow this val job = scope launch states onEach newState gt updates emit DistributedMergeable Update source newState launchIn this updates onEach update gt println update if update source == source println Same source $update return onEach if update value == states value println Same state $update return onEach val merged = states value merge update value println Merged $update gt $merged states value = merged launchIn this return DistributedMergeable states updates job ``` Is there a way to make sure these collectors are running before returning the `DistributedMergeable` I tried something like this ``` await start scope launch while job children any it isActive delay 1 join ``` But that feels wrong