Android Kotlin Testing

Android Kotlin — Testing Module

Parent kit: ../../SKILL.md · Index: ../../AGENTS.md

Read First

File	When
../../references/11-testing.md	Turbine, fakes, Compose test tags
../../references/05-hilt-di.md	TestInstallIn modules
../../references/13-release-checklist.md	Pre-ship checklist

ViewModel Test Template

@OptIn(ExperimentalCoroutinesApi::class)
class FeatureViewModelTest {

    @get:Rule
    val mainDispatcherRule = MainDispatcherRule()

    private val fakeRepo = FakeFeatureRepository()
    private lateinit var viewModel: FeatureViewModel

    @Before
    fun setup() {
        viewModel = FeatureViewModel(fakeRepo)
    }

    @Test
    fun `refresh success clears loading`() = runTest {
        fakeRepo.syncResult = Result.success(Unit)

        viewModel.onEvent(FeatureUiEvent.Refresh)

        viewModel.state.test {
            skipItems(1)
            val loading = awaitItem()
            assertTrue(loading.isLoading)
            val done = awaitItem()
            assertFalse(done.isLoading)
            assertNull(done.error)
        }
    }
}

Fake Over Mock

class FakeFeatureRepository : FeatureRepository {
    var syncResult: Result<Unit> = Result.success(Unit)
    private val items = MutableStateFlow<List<Feature>>(emptyList())

    override fun observeItems(): Flow<List<Feature>> = items
    override suspend fun sync(): Result<Unit> = syncResult
}

Prefer fakes implementing real interfaces — tests behavior, not interaction order.

Compose UI Test

class FeatureScreenTest {
    @get:Rule
    val composeRule = createComposeRule()

    @Test
    fun showsEmptyState() {
        composeRule.setContent {
            AppTheme {
                FeatureContent(
                    state = FeatureUiState(items = emptyList()),
                    onEvent = {}
                )
            }
        }
        composeRule.onNodeWithTag("feature_empty").assertIsDisplayed()
    }
}

Test stateless FeatureContent, not ViewModel-integrated screen.

What to Test vs Skip

Always test	Usually skip
ViewModel state transitions	Room generated SQL
Repository mappers	Hilt graph wiring (compile-time)
Error paths (Result.failure)	Pixel-perfect screenshots
Critical user flows (instrumented)	Third-party SDK internals

CI Gate

Repo skill validation must pass before merge:

python3 scripts/validate_skills.py --strict