InstantTaskExecutorRule

SuperHeroesViewModelTest.kt

class SuperHeroesViewModelTest {

    @get:Rule
    val instantTaskExecutorRule = InstantTaskExecutorRule()

    private val superHeroesRepository = mockk<SuperHeroesRepository>()
    private lateinit var superHeroesViewModel: SuperHeroesViewModel

    private val listOfSuperHeroes = listOf(SuperHero("Iron Man"), SuperHero("Hulk"))
    private val successfulSuperHeroesResult = Result.Success(listOfSuperHeroes)

    @Before
    fun setUp() {
        every { superHeroesRepository.loadSuperHeroes() } returns successfulSuperHeroesResult
        superHeroesViewModel = SuperHeroesViewModel(superHeroesRepository)
    }

    @Test
    fun `when tasks are received from repository then should load to the view`() {
        with(superHeroesViewModel) {
            loadSuperHeroes()
            verify { superHeroesRepository.loadSuperHeroes() }

            val receivedSuperHeroes = superHeroesLiveData.testObserver().observedValues.get(0)
            assertThat(receivedSuperHeroes).isNotEmpty().hasSize(listOfSuperHeroes.size)
        }
    }
}

SuperHeroesViewModelTest2.kt

class SuperHeroesViewModelTest {

    @get:Rule
    var instantExecutorRule = InstantTaskExecutorRule()
    @Mock
    private lateinit var superHeroesRepository: SuperHeroesRepository

    private lateinit var superHeroesViewModel: SuperHeroesViewModel

    @Before
    fun setUp() {
        MockitoAnnotations.initMocks(this)

        superHeroesViewModel = SuperHeroesViewModel(superHeroesRepository)
    }

    @Test
    fun `when tasks loaded from repository then should delegate to view callback`() {
        with(superHeroesViewModel) {
            loadSuperHeroes()
            verify(superHeroesRepository).loadSuperHeroes()
        }
    }
}