Coroutine Test

Test.kt

class AccountOwnerTypeViewModelTest {

    @Rule
    @JvmField
    val rule = InstantTaskExecutorRule()

    val mainThreadSurrogate = newSingleThreadContext("UI thread")

    @Before
    fun setUp() {
        Dispatchers.setMain(mainThreadSurrogate)
    }

    @After
    fun tearDown() {
        Dispatchers.resetMain()
        mainThreadSurrogate.close()
    }

    @Test
    fun bar(){
            val viewModel = ViewModel()
            val acc  = mutableListOf<Int>()
            viewModel.foo.observeForever{acc.add(it)}
            runBlocking {
                repeat(100) {
                    viewModel.start()
                }
            }
            assertEquals(acc, IntArray(100){it}.asList())
    }

    class ViewModel : CoroutineScope {
        private val job = Job()
        override val coroutineContext: CoroutineContext = job + Dispatchers.Main

        val foo = MutableLiveData<Int>()

        private var i = 0
        fun start(){
            launch{
                foo.postValue(i++)
            }
        }
    }
}