Coroutines and Testing

PseudoCodeTestExample.kt

////////////
// Kotlin //
////////////
implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk8:1.3.31"
implementation "org.jetbrains.kotlinx:kotlinx-coroutines-core:1.2.1"
implementation "org.jetbrains.kotlinx:kotlinx-coroutines-android:1.2.1"

////////////////
// Unit Tests //
////////////////
testImplementation "junit:junit:4.12"
testImplementation "org.mockito:mockito-core:2.27.0"
testImplementation "org.mockito:mockito-inline:2.27.0"
testImplementation "com.nhaarman.mockitokotlin2:mockito-kotlin:2.1.0"
testImplementation "org.jetbrains.kotlinx:kotlinx-coroutines-test:1.2.1"


sealed class Data {
    class Success(content: String) : Data()
    class Failure() : Data()
}

class Repository() {
    
    suspend fun fetchRemoteData() : Data {

        return try {
            //pseudocode that takes time to execute, in this case a Firebase Task
            val content = Firebase.get("whatever").await
            Success(content)
        } catch (exception: FirebaseException) {
           Failure()
        }
    }

}

class MyPresenter(val view: IMyView, val repository: Repository): CoroutineScope {
    
    val job = Job()

    override val coroutineContext: CoroutineContext
        get() = Dispatchers.Main + job


    fun doStuff() {

        launch {
            view.showProgress()
            val data = repository.fetchRemoteData()
            view.populateScreen(data)
            view.hideProgress()    
        }

    }


    fun onViewDestroy() {
        job.cancel()
    }


    interface IMyView {

        fun showProgress()

        fun populateScreen(data: Data)

        fun hideProgress()

    }

}


class MyPresenterTest() {
    
    val mockView: IMyView = mock()
    val mockRepo: Repo = mock()
    val mockData: Data = mock()


    val testCoroutineContext = TestCoroutineDispatcher()

    lateinit var presenter: MyPresenter

    @Before
    fun setUp() {
        Dispatchers.setMain(testCoroutineContext as CoroutineDispatcher)
        presenter = MyPresenter(mockView, mockRepo)
    }

    @After
    fun tearDown() {
        presenter.onViewDestroy()
        Dispatchers.resetMain()
    }

    @Test
    fun testDoStuff() = testCoroutineContext.runBlockingTest {

        //given
        whenever(mockRepo.fetchRemoteData()).thenReturn(mockData)

        //when
        presenter.doStuff()

        //then
        verify(mockView).showProgress()
        verify(mockRepo).fetchRemoteData()
        verify(mockView).populateScreen(mockData)
        verify(mockView).hideProgress()
    }

}