Hi team, hope you don’t mind a Cashapp/Turbine que...

# squarelibraries

[Tim Malseed]

Hi team, hope you don’t mind a Cashapp/Turbine question here.

This is a cross-post from #coroutines b/c I’m not quite sure if Turbine is influencing the outcome here..

I’m having trouble with a unit test. I’m trying to validate the behaviour of a StateFlow. But, the StateFlow is only in this particular state until a certain suspend function completes.

During testing, my test double uses a delay to simulate a long running task. But, due to the nature of runBlockingTest() , this delay is skipped, so this function completes immediately, and the StateFlow essentially bypasses the value I’m trying to test.

[Tim Malseed]

sealed class ViewState {
    object None : ViewState()
    object Loading : ViewState()
    object Some : ViewState()
}

class Foo {
    val viewState = MutableStateFlow<ViewState>(ViewState.None)

    fun updateViewState() {
        viewState.value = ViewState.Loading

        viewState.value = someLongRunningOperation()
    }

    private suspend fun somePotentiallyLongRunningOperation(): ViewState {
        delay(5000)
        return ViewState.Some
    }
}

@Test
fun myTest() = runBlockingTest {
    foo.viewState.test {
        foo.updateViewState()

        assertThat(awaitItem()).isInstanceOf(ViewState.Loading::class.java) // Fails. ViewState is ViewState.Some

        cancelAndConsumeRemainingEvents()
    }
}

[Paul Woitaschek]

As it's deprecated, try runTest first

[Tim Malseed]

The above is psuedo code, and I hadn’t actually written that exact test. Looks like it actually is working, so perhaps there’s some other problem in my production code. I need to get better at actually writing small repros.

[Tim Malseed]

Moving to runTest() does seem to solve most of my problems, and revealed a few new ones that make me wonder how the tests ever passed at all!

[Paul Woitaschek]

Haha yes, that was my experience as well.