How to inject coroutine dispatcher in Unit Test - using Koin

I am injecting my dispatcher, using Koin, into my classes

Extract of one class using Koin

class LogsWorker(
    val context: Context,
    workerParameters: WorkerParameters
) : CoroutineWorker(context, workerParameters), KoinComponent {

    private val ioDispatcher: CoroutineDispatcher by inject()


val appModule = module {
    factory { provideIoDispatcher() }

private fun provideIoDispatcher(): CoroutineDispatcher = Dispatchers.IO

If I want to unit test my LogsWorker class, I need to inject a coroutineTestDispatcher. How could I do that? I don't find any example anywhere.

1 answer

  • answered 2021-07-28 07:56 Róbert Nagy

    You need to override that bean definition in your testing, when you are loading you are starting koin and loading the modules.

    You can do that with: factory(override = true) { provideYourTestingDispatcher }

    Read more about it here

    Although the above could work, I just find it more elegant to use constructor injection instead, for ex:

    class LogsWorker(
        val context: Context,
        workerParameters: WorkerParameters,
        private val ioDispatcher: CoroutineDispatcher
    ) : CoroutineWorker(context, workerParameters)

    Then you can just specify the definition for LogsWorker in koin, such as:

    factory { (context: Context, workerParameters: WorkerParameters) -> LogsWorker(context, workerParameters, get()) }

    And in testing, you can just simply pass in the testing dispatcher. More info about this:

    UPDATE: override is deprecated, you could use KoinApplication.allowOverride(true) instead

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