Unit tests and concurrency 1

utc_1.kt

// Emits Loading then Content or Problem
private fun requestData(): Observable<ViewState> =
    service.firstApiCall()
        .observeOn(Schedulers.computation())
        .map { it.message }
        .flatMap(this::secondApiCall)
        .map<ViewState> { ViewState.Content(it) }
        .startWith(Single.just(ViewState.Loading))
        .onErrorReturn { ViewState.Problem }
        .toObservable()

// Concurrently executes secondApiCall for each element in list. 
// Transforms the result to ViewEntity, combines everything in a list
private fun secondApiCall(list: List<String>): Single<List<ViewEntity>> =
    Observable.fromIterable(list)
        .concatMapEager { item ->
            service.secondEndpoint(item)
                .observeOn(Schedulers.computation())
                .map { it.message }
                .map { ViewEntity(item, it.toHttpUrl()) }
                .onErrorReturn { DogViewEntity(item, null) }
                .toObservable()
        }
        .toList()