Hello everyone, is there a way to unit test a shared flow that emits before collecting, for instance...

# android

[Eury Perez]

Hello everyone, is there a way to unit test a shared flow that emits before collecting, for instance: I'm emitting in the viewModel's init block. Here's what I'm trying:

val values = mutableListOf<Int>()
val sharedFlow = MutableSharedFlow<Int>()
sharedFlow.emit(0)
val job = launch { // <------
    stateFlow.collect {
        values.add(it)
    }
}
runCurrent()
sharedFlow.emit(1)
runCurrent()
sharedFlow.emit(2)
runCurrent()
sharedFlow.emit(3)
runCurrent()
job.cancel()

assertEquals(listOf(0, 1, 2, 3), values)

A similar test passes with stateflow

[Thiago Souto]

You can use Turbine from CashApp

https://github.com/cashapp/turbine

[Eury Perez]

It won't work anyway, check this https://kotlinlang.slack.com/archives/C1CFAFJSK/p1682341379857279?thread_ts=1682340884.092909&cid=C1CFAFJSK

[zsmb]

With a SharedFlow if there’s no cache configured you have to have the collector ready in time to collect it, otherwise you’ll just miss it.

Also, slightly unrelated: you can launch the collecting coroutine in backgroundScope to avoid having to keep a reference to its job and cancelling it manually at the end of the test.