android-testing

Android Testing

No tests = not production-ready. These rules cover the complete Android testing stack.

Setup — all testing dependencies

[versions]
junit = "4.13.2"
junitExt = "1.2.1"
coroutinesTest = "1.9.0"
mockk = "1.13.12"
turbine = "1.1.0"
roborazzi = "1.27.0"
hiltTesting = "2.52"

[libraries]
junit = { group = "junit", name = "junit", version.ref = "junit" }
mockk = { group = "io.mockk", name = "mockk", version.ref = "mockk" }
mockk-android = { group = "io.mockk", name = "mockk-android", version.ref = "mockk" }
kotlinx-coroutines-test = { group = "org.jetbrains.kotlinx", name = "kotlinx-coroutines-test", version.ref = "coroutinesTest" }
turbine = { group = "app.cash.turbine", name = "turbine", version.ref = "turbine" }
androidx-junit = { group = "androidx.test.ext", name = "junit", version.ref = "junitExt" }
hilt-android-testing = { group = "com.google.dagger", name = "hilt-android-testing", version.ref = "hiltTesting" }
room-testing = { group = "androidx.room", name = "room-testing", version.ref = "room" }
roborazzi = { group = "io.github.takahirom.roborazzi", name = "roborazzi", version.ref = "roborazzi" }
roborazzi-compose = { group = "io.github.takahirom.roborazzi", name = "roborazzi-compose", version.ref = "roborazzi" }

// build.gradle.kts
testImplementation(libs.junit)
testImplementation(libs.mockk)
testImplementation(libs.kotlinx.coroutines.test)
testImplementation(libs.turbine)
testImplementation(libs.room.testing)
androidTestImplementation(libs.androidx.junit)
androidTestImplementation(libs.hilt.android.testing)
androidTestImplementation(libs.mockk.android)
androidTestImplementation(libs.roborazzi)
androidTestImplementation(libs.roborazzi.compose)
kspAndroidTest(libs.hilt.compiler)

Rule 1: ViewModel tests — pure unit tests

class HomeViewModelTest {
    // Replace Main dispatcher with test dispatcher
    @get:Rule
    val mainDispatcherRule = MainDispatcherRule()

    private val fakeRepository = FakeItemRepository()
    private lateinit var viewModel: HomeViewModel

    @Before
    fun setUp() {
        viewModel = HomeViewModel(
            getItems = GetItemsUseCase(fakeRepository),
            toggleFavorite = ToggleFavoriteUseCase(fakeRepository)
        )
    }

    @Test
    fun `initial state is Loading`() = runTest {
        viewModel.uiState.test {
            assertEquals(HomeUiState.Loading, awaitItem())
            cancelAndIgnoreRemainingEvents()
        }
    }

    @Test
    fun `loads items successfully`() = runTest {
        fakeRepository.setItems(listOf(sampleItem))

        viewModel.uiState.test {
            skipItems(1) // skip Loading
            val state = awaitItem()
            assertTrue(state is HomeUiState.Success)
            assertEquals(1, (state as HomeUiState.Success).items.size)
        }
    }

    @Test
    fun `shows error when loading fails`() = runTest {
        fakeRepository.setShouldFail(true)

        viewModel.uiState.test {
            skipItems(1) // skip Loading
            assertTrue(awaitItem() is HomeUiState.Error)
        }
    }

    @Test
    fun `emits navigation event on item click`() = runTest {
        viewModel.events.test {
            viewModel.onItemClick("item-123")
            assertEquals(HomeEvent.NavigateToDetail("item-123"), awaitItem())
        }
    }
}

// MainDispatcherRule — required for every ViewModel test
class MainDispatcherRule(
    private val dispatcher: TestDispatcher = UnconfinedTestDispatcher()
) : TestWatcher() {
    override fun starting(description: Description) {
        Dispatchers.setMain(dispatcher)
    }
    override fun finished(description: Description) {
        Dispatchers.resetMain()
    }
}