Testing

A layered architecture is also a testable architecture. Most logic can be covered by fast JVM unit tests; only UI behavior needs the Compose test rule or an emulator.

The testing pyramid

Test type	Runs on	Speed	Tests
Unit	JVM	fast	ViewModels, use cases, repositories, pure logic
Compose UI	JVM (Robolectric) or device	medium	composable behavior
Instrumented / E2E	emulator/device	slow	full flows, Room, navigation

CI runs the unit (and Robolectric-backed Compose) tests; instrumented tests are run locally.

Unit-testing a ViewModel

Inject a fake repository and a test dispatcher:

class FakeArticleRepository(private val data: List<Article>) : ArticleRepository {
    override suspend fun articles(): List<Article> = data
}

@OptIn(ExperimentalCoroutinesApi::class)
class ArticlesViewModelTest {
    @Test
    fun `load emits Success`() = runTest {
        Dispatchers.setMain(StandardTestDispatcher(testScheduler))
        val vm = ArticlesViewModel(FakeArticleRepository(listOf(Article(1, "t", "b"))))

        vm.load()
        advanceUntilIdle()

        val state = vm.uiState.value
        assertTrue(state is ArticlesUiState.Success)
        Dispatchers.resetMain()
    }
}

The example app’s ArticlesViewModelTest follows this exact pattern and runs in CI.

Compose UI tests

class CounterScreenTest {
    @get:Rule val rule = createComposeRule()

    @Test
    fun increments() {
        rule.setContent { CounterScreen() }
        rule.onNodeWithText("Increment").performClick()
        rule.onNodeWithText("Count: 1").assertExists()
    }
}

Run these on the JVM with Robolectric (testImplementation) or on a device as instrumented tests. The example app’s CounterScreenTest is exactly this — a Robolectric-backed Compose UI test that runs in CI (no emulator):

@RunWith(RobolectricTestRunner::class)
@GraphicsMode(GraphicsMode.Mode.NATIVE)
@Config(sdk = [34])
class CounterScreenTest {
    @get:Rule val composeTestRule = createComposeRule()

    @Test
    fun clickingIncrement_incrementsCount() {
        composeTestRule.setContent { CounterScreen(viewModel = CounterViewModel()) }
        composeTestRule.onNodeWithText("Increment").performClick()
        composeTestRule.onNodeWithText("Count: 1").assertIsDisplayed()
    }
}

It needs androidx.compose.ui:ui-test-junit4 + ui-test-manifest, Robolectric, and testOptions { unitTests { isIncludeAndroidResources = true } }.

Testing flows

Use runTest and collect, or libraries like Turbine:

@Test
fun emits() = runTest {
    val values = repository.articlesFlow().first()
    assertEquals(2, values.size)
}

Exercises

1. Write a FakeArticleRepository that throws, and assert the ViewModel emits Error.

2. Add a Compose UI test asserting the Reset button returns the count to 0.

---

Previous: Modularization & Build Variants · Next: Performance & Best Practices