Testing strategy

Testing Strategy

Convention Plugins

Plugin	Use for	Provides
android.test.unit	ViewModel, UseCase, Repository	JUnit + MockK + Coroutines Test + Truth
android.test.instrumentation	Compose UI tests	AndroidJUnit4 + Compose Test
android.test.robolectric	Android unit tests	Robolectric

Add to build.gradle.kts:

plugins {
    alias(libs.plugins.android.feature.compose)
    alias(libs.plugins.android.test.unit)  // Add for tests
}

Test File Locations

feature/<name>/src/test/           -> ViewModel unit tests
domain/usecase/src/test/           -> UseCase unit tests
data/remote-data/src/test/         -> Repository unit tests
feature/<name>/src/androidTest/    -> Compose UI tests

1. ViewModel Unit Test

@OptIn(ExperimentalCoroutinesApi::class)
class SampleViewModelTest {

    @get:Rule
    val mainDispatcherRule = MainDispatcherRule()

    private lateinit var viewModel: SampleViewModel
    private val getSampleUseCase: GetSampleUseCase = mockk()

    @Before
    fun setup() {
        every { getSampleUseCase() } returns flowOf(PagingData.empty())
        viewModel = SampleViewModel(getSampleUseCase)
    }

    @Test
    fun `initial state should have paging flow set`() {
        assertThat(viewModel.uiState.value.items).isNotNull()
    }

    @Test
    fun `OnItemClick should emit NavigateToDetail effect`() = runTest {
        val item = SampleModel(id = "123", name = "Test Item")

        viewModel.onTriggerEvent(SampleViewEvent.OnItemClick(item))

        assertThat(viewModel.effectState.value)
            .isInstanceOf(SampleViewEffect.NavigateToDetail::class.java)
        assertThat((viewModel.effectState.value as SampleViewEffect.NavigateToDetail).id)
            .isEqualTo("123")
    }
}

MainDispatcherRule

Located in the test source of the first feature module that uses it. Copy to each test module that needs it:

@OptIn(ExperimentalCoroutinesApi::class)
class MainDispatcherRule(
    private val testDispatcher: TestDispatcher = UnconfinedTestDispatcher()
) : TestWatcher() {

    override fun starting(description: Description) {
        Dispatchers.setMain(testDispatcher)
    }

    override fun finished(description: Description) {
        Dispatchers.resetMain()
    }
}

2. UseCase Unit Test

class GetDetailUseCaseTest {

    private val repository: ItemRepository = mockk()
    private lateinit var useCase: GetDetailUseCaseImpl

    @Before
    fun setup() {
        useCase = GetDetailUseCaseImpl(repository)
    }

    @Test
    fun `invoke should return item from repository`() = runTest {
        val expectedItem = Item(id = "1", name = "Test")
        coEvery { repository.getItemDetail("1") } returns flowOf(
            DataState.Success(expectedItem)
        )

        useCase(GetDetailParam(id = "1")).collect { state ->
            when (state) {
                is DataState.Success -> assertThat(state.data).isEqualTo(expectedItem)
                else -> fail("Expected Success")
            }
        }
    }

    @Test
    fun `invoke should propagate repository errors`() = runTest {
        coEvery { repository.getItemDetail("1") } returns flowOf(
            DataState.Error(AppError.ServerError(500))
        )

        useCase(GetDetailParam(id = "1")).collect { state ->
            assertThat(state).isInstanceOf(DataState.Error::class.java)
        }
    }
}

3. Repository Unit Test

class ItemRepositoryImplTest {

    private val remoteDataSource: ItemRemoteDataSource = mockk()
    private val itemMapper: ItemMapper = mockk()
    private lateinit var repository: ItemRepositoryImpl

    @Before
    fun setup() {
        repository = ItemRepositoryImpl(remoteDataSource, itemMapper)
    }

    @Test
    fun `getItemDetail should map DTO to domain model`() = runTest {
        val dto = ItemDto(id = "1", name = "Test")
        val domain = Item(id = "1", name = "Test")
        coEvery { remoteDataSource.getItemById("1") } returns flowOf(DataState.Success(dto))
        every { itemMapper.toDomain(dto) } returns domain

        repository.getItemDetail("1").collect { state ->
            when (state) {
                is DataState.Success -> assertThat(state.data).isEqualTo(domain)
                else -> {}
            }
        }
    }
}

4. Compose UI Test

@HiltAndroidTest
class SampleScreenTest {

    @get:Rule
    val composeTestRule = createComposeRule()

    @Test
    fun `SampleScreenInternal displays content`() {
        val fakeViewModel = FakeBaseViewModel<SampleViewState, SampleViewEvent, SampleViewEffect>(
            initialState = SampleViewState()
        )

        composeTestRule.setContent {
            TemplateThemePreview { SampleScreenInternal(viewModel = fakeViewModel) }
        }

        composeTestRule.onNodeWithText("Sample").assertIsDisplayed()
    }

    @Test
    fun `loading state shows loading indicator`() {
        val fakeViewModel = FakeBaseViewModel<SampleViewState, SampleViewEvent, SampleViewEffect>(
            initialState = SampleViewState(),
            initialLoading = true
        )

        composeTestRule.setContent {
            TemplateThemePreview { SampleScreenInternal(viewModel = fakeViewModel) }
        }

        composeTestRule.onNode(hasTestTag("loading_indicator")).assertIsDisplayed()
    }
}

Test Naming Convention

Pattern: `[method/action] [condition] should [expected result]`

fun `onTriggerEvent OnItemClick should set NavigateToDetail effect`()
fun `collectDataState with server error should call onError`()
fun `initial state should have empty list and loading false`()

Test Priority

High (test first)

1. ViewModels - onTriggerEvent(), state transitions, effect emissions
2. UseCases with business logic
3. ExceptionMapper - exception -> AppError mappings
4. ErrorHandler - AppError -> string resource mappings

Medium

5. Repository implementations - DTO -> Domain, flow logic
6. BaseDataSource strategies - success/error flows

Lower

7. Compose UI tests - screen rendering, user interactions
8. Navigation tests