Kotlinx.coroutines: UI android context and Looper.getMainLooper() not mocked

[milk-machine]

Cant call code with UI context usage in android unit tests. Test throw:
Caused by: java.lang.RuntimeException: Method getMainLooper in android.os.Looper not mocked.

[milk-machine]

Need opportunity to substitute context.

[elizarov]

You can try to define a function that returns a context and use it in your code. Then you'll be able to mock it. Will it work for your case?

[milk-machine]

Currently i use follow solution:

import kotlin.coroutines.experimental.CoroutineContext
import kotlin.coroutines.experimental.EmptyCoroutineContext
import kotlinx.coroutines.experimental.android.UI as mainLooperContext

val UI by lazy { initializationBlock() }

private var initializationBlock: () -> CoroutineContext = { mainLooperContext }

fun stubUiContext() {
    initializationBlock = { EmptyCoroutineContext }
}

But perhaps this problem will appear not only for me in the future.

[elizarov]

What kind of solution you'd like in kotlinx.coroutines for that?

[dmytrodanylyk]

@milk-machine I think that's not related to coroutines. Just inject context, like you do in Rx Java https://medium.com/@peter.tackage/an-alternative-to-rxandroidplugins-and-rxjavaplugins-scheduler-injection-9831bbc3dfaf

[matejdro]

What kind of solution you'd like in kotlinx.coroutines for that?

I think good solution would be in-built mechanism to replace any scheduler (UI in this case) with instant execution scheduler for Unit tests, similar to how RxJava does this with RxAndroidPlugins.

While solution that @dmytrodanylyk mentions works, it creates a lot of additional unnecessary boilerplate code.

[JakeWharton]

I am very much against that. RxJava got it wrong. We already have a mechanism for that: inversion of control.

[elizarov]

Closing this issue. We will not providing ability to replace standard contexts in the library.

[johnjohndoe]

:eyes: Related article: Unit testing with MutableLiveData