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kotlinlang

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&lt;SomeData&gt;()
    ...
    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&lt;AViewModel&gt; { ... }
    ...
    fun onViewCreate(...) {
        button.setOnclickListener {
            viewModel.doSomething()
        }
        
        viewModel.liveData.observe(viewLifecycle, Observer { result -&gt;
        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&lt;out DaggerApplication&gt; {
        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 :point_right::skin-tone-3: <https://github.com/google/iosched/tree/adssched/mobile/src/androidTest/java/com/google/samples/apps/iosched/tests|https://github.com/google/iosched/tree/adssched/mobile/src/androidTest/java/com/google/samples/apps/iosched/tests>

And don't forget to add dagger for instrumentation tests too 
```
kaptAndroidTest "com.google.dagger:dagger-compiler:$rootProject.dagger"
    kaptAndroidTest "com.google.dagger:dagger-android-processor:$rootProject.dagger"
```

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

<https://medium.com/androiddevelopers/android-testing-with-espressos-idling-resources-and-testing-fidelity-8b8647ed57f4>

I also double checked with <@UDFLD19DL> and he also suggested as I mentioned

Very informative thank you very much :heart: