Presenter testing with Composition Local Providers

[matthewbahr-clear]

Hey wanted to bring up a use case that I ran into recently with an offer building out something more formal if there's interest.

The TLDR is with some small tweaks you can test presenters with composition local providers.

We have an entirely isolated flow (1 public entry screen then everything else is internal) so we added a few contextual fields as composition locals that we didn't want to pipe around from screen to screen.

Since the final presenter ends up interpreting that composable context and then performing an action based on the result of that we needed to be able to provide that field in unit tests.

So I roughed in a pretty basic, small function that allows you to provide composition locals with the caveat that the initial UIState will be null, unlike other current circuit turbines.

  suspend fun <UiState : CircuitUiState> Presenter<UiState>.test(
    vararg locals: ProvidedValue<*>,
    timeout: Duration? = null,
    name: String? = null,
    block: suspend ReceiveTurbine<UiState?>.() -> Unit,
  ) {
    moleculeFlow(
      RecompositionMode.Immediate,
    ) {
      var result: UiState? by remember {
        mutableStateOf(null)
      }
      CompositionLocalProvider(*locals) {
        result = present()
      }
      result
    }.test(timeout, name) {
      block()
    }
  }

Would anyone else find this useful or is this use case too niche to drop into the toolbox?

[stagg]

Typically seen this achieved using presenterTestOf and withCompositionLocalProvider.

val presenter  = .. 
presenterTestOf(
  presentFunction = {
    withCompositionLocalProvider(..) {
      presenter.present()
    }
  }
) {
  awaitItem()
}

Might be worth having that in a new Presenter<UiState>.test method, PR welcome!