Hi all, how do you guys test a StateFlow in Android, for example, a ViewModel?

# test

[Manuel Lorenzo]

Hi all, how do you guys test a StateFlow in Android, for example, a ViewModel?

[Manuel Lorenzo]

with LiveData, it was easy, as we could observer forever but with a StateFlow, I don’t see any way of doing something similar

[kevin.cianfarini]

take a look at Turbine by square. It's fantastic. https://github.com/cashapp/turbine

[kevin.cianfarini]

also you'll probably want to be looking at runBlocking for your tests

[kevin.cianfarini]

...and also avoiding viewModelScope. Testing becomes a bit easier if you inject a scope into the viewmodel via dependency injection and then implement CoroutineScope via interface delegation

[kevin.cianfarini]

let me dig you up an example.

[kevin.cianfarini]

class MyViewModel @Inject constructor(
    @Named("viewModelScope") scope: CoroutineScope
) : ViewModel(), CoroutineScope by scope {

    override fun onCleared() {
        super.onCleared()
        cancel()
    }
}

@Test fun testFoo() = runBlocking { // this: CoroutineScope
    val viewModel = MyViewModel(this)

    viewModel.someFlow.test { ... }
}

[Manuel Lorenzo]

thanks @kevin.cianfarini! I tried but I get this:

java.lang.NoSuchMethodError: app.cash.turbine.FlowTurbineKt.test-f_gJSvk$default(Lkotlinx/coroutines/flow/Flow;DLkotlin/jvm/functions/Function2;Lkotlin/coroutines/Continuation;ILjava/lang/Object;)Ljava/lang/Object;

[kevin.cianfarini]

That's strange. Did you add is as a testImplementstion? Also you can try asking questions over at #squarelibraries

[Manuel Lorenzo]

yep I did

[Manuel Lorenzo]

ah OK, I can ask there, thanks!