Cannot dispatch action error when testing with turbine about flowredux

[gabrielittner]

This is happening because of the general behavior of StateFlow. Since StateFlow has its own initial value that will get emitted immediately to Turbine. So the awaitItem is handled and dispatch is called. The issue is that that doesn't mean that stateIn has started collecting the upstream state yet and because StateFlow has a builtIn distinctUntilChanged there is also no way to wait for the actual first emission of FlowReduxStateMachine. There are a few solutions for this:

• use state instead of stateFlow in tests, that way the first emission for awaitItem comes from FlowReduxStateMachine and the on/dispatch is guaranteed to work
• replace StateFlow with SharedFlow by using shareIn(..., replay = 1), similar to the above but lets you use the shared flow for tests so that the test is closer to a real consumer
• have a different initial state for the StateFlow and the StateMachine, probably not a nice solution

I would also generally recommend one of the first 2 in tests. StateFlow has some things like conflation of values that can easily make tests flaky since you might not get in between emissions sometimes.

[JBokMan]

Thank you so much!

We chose the second solution. In the example code the change is just from

val stateFlow: StateFlow<MachineState> = state.stateIn(
    scope = CoroutineScope(Dispatchers.Default),
    started = SharingStarted.Eagerly,
    initialValue = initialState
)

to

val stateFlow: SharedFlow<MachineState> = state.shareIn(
    scope = CoroutineScope(Dispatchers.Default),
    started = SharingStarted.Eagerly,
    replay = 1
)