Testable Kotlin objects that uses a dispatcher in init block? - kotlin-coroutines

Question

I have a class that looks like this:
object SomeRepository {
private val logger = Logger(this)
private val flow: MutableStateFlow<List<SomeClass>> = MutableStateFlow(listOf())
init {
GlobalScope.launch(Dispatchers.IO) {
// some code
}
}
fun list() = flow.value
fun observe(): StateFlow<List<SomeClass>> = flow
}
It is recommended to inject dispatchers in tests.
Also, there is a risk to get weird problems such as AppNotIdleException if not following this practice.
One option would be to make these into variables and add setters, but not very nice. Also it creates a race condition (init-block vs setters):
object SomeRepository {
private val logger = Logger(this)
private val flow: MutableStateFlow<List<SomeClass>> = MutableStateFlow(listOf())
private var coroutineScope: CoroutineScope = GlobalScope
private var dispatcher: CoroutineDispatcher = Dispatchers.IO
init {
dispatcher.launch(coroutineScope) {
// some code
}
}
fun list() = flow.value
fun observe(): StateFlow<List<SomeClass>> = flow
#VisibleForTesting
fun setDispatcher(dispatcher: CoroutineDispatcher) {
this.dispatcher = dispatcher
}
#VisibleForTesting
fun setCoroutineScope(coroutineScope: CoroutineScope) {
this.coroutineScope = coroutineScope
}
}
Version that avoids the race condition (test needs to explicitly invoke init()):
object SomeRepository {
private val logger = Logger(this)
private val flow: MutableStateFlow<List<SomeClass>> = MutableStateFlow(listOf())
private var coroutineScope: CoroutineScope = GlobalScope
private var dispatcher: CoroutineDispatcher = Dispatchers.IO
init {
// var isInTesting = Build.FINGERPRINT == "robolectric"
if (!isInTesting) {
init()
}
}
#VisibleForTesting
fun init() {
dispatcher.launch(coroutineScope) {
// some code
}
}
fun list() = flow.value
fun observe(): StateFlow<List<SomeClass>> = flow
#VisibleForTesting
fun setDispatcher(dispatcher: CoroutineDispatcher) {
this.dispatcher = dispatcher
}
#VisibleForTesting
fun setCoroutineScope(coroutineScope: CoroutineScope) {
this.coroutineScope = coroutineScope
}
}
How can I inject a coroutine scope and dispatcher to my tests and avoid variables?