Hi Guys, I was wondering whether anyone has been testing coroutine with Espresso? it is a common pattern with MVVM to do something like:

class AViewModel() : ViewModel() {
    val liveData = MutableLiveData<SomeData>()
    ...
    fun doSomething() {
        viewModelScope.launch {
            //... do some long operation ....
            liveData.value = resultOfLongOperation
        }
    }
}

and observe the live data in Fragment or Activity like:

...
    val viewModel by viewModels<AViewModel> { ... }
    ...
    fun onViewCreate(...) {
        button.setOnclickListener {
            viewModel.doSomething()
        }
        
        viewModel.liveData.observe(viewLifecycle, Observer { result ->
        textView.text = result
    })
    }
...

I was wondering how to do UI test for the Code above. Since the

doSomething()

takes a while to complete, my

Espresso

test is failing. Can anyone share how they do their test? Thank you very much.

You have to inject the dispatcher and use

AsyncTask.THREAD_POOL_EXECUTOR.asCoroutineDispatcher()

in UI tests since espresso knows there is a background task and waits for that task to be finished with this dispatcher. If you are using dagger 1- Create a

TestAppComponent

and override Coroutine dispatchers with a module and use

AsyncTask.THREAD_POOL_EXECUTOR.asCoroutineDispatcher() for <http://Dispatcers.IO|Dispatcers.IO> and Dispatchers.Default

2- Create a

TestApplication

which overrides your custom

Application

class and inject

DaggerTestAppComponent

like

override fun applicationInjector(): AndroidInjector<out DaggerApplication> {
        return DaggerTestAppComponent.builder().create(this)
    }

3- Create a

CustomTestRunner

and override

newApplication

to be able to use

TestApplication

4- Give this

CustomTestRunner

in your gradle file as a test runner You can check it out from Android Developer Summit app 👉🏼 https://github.com/google/iosched/tree/adssched/mobile/src/androidTest/java/com/google/samples/apps/iosched/tests

This is the interesting bit

AsyncTask.THREAD_POOL_EXECUTOR.asCoroutineDispatcher()

I never knew you could do that.. hmmm... I will do try that. I also came across this github thread here: https://github.com/Kotlin/kotlinx.coroutines/issues/242 I'm kinda curious whatcha think about it.

Idling resource needs refactoring the production code which I dont prefer. Think it like you have a piece of code which does nothing in production

Very informative thank you very much ❤️

Np 😄 happy to help