fix(android-native-dev): Add testing for android-native-dev skill
This commit is contained in:
utzcoz
554
skills/android-native-dev/references/testing.md
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554
skills/android-native-dev/references/testing.md
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# Testing
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Detailed examples and patterns for each Android test layer. Read the section relevant to the layer you're working with.
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## Table of Contents
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1. [Local Unit Tests (JUnit + Robolectric)](#1-local-unit-tests-junit--robolectric)
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2. [Instrumentation Tests (Espresso)](#2-instrumentation-tests-espresso)
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3. [UI Automator (Cross-App & System UI)](#3-ui-automator-cross-app--system-ui)
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4. [Compose UI Testing](#4-compose-ui-testing)
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5. [Gradle Managed Devices](#5-gradle-managed-devices)
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---
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## 1. Local Unit Tests (JUnit + Robolectric)
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Local tests live in `src/test/` and run on the JVM — no emulator needed, so they're fast (milliseconds each). Use them for ViewModels, Repositories, mappers, validators, and any pure logic.
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### Basic ViewModel Test
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```kotlin
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class CounterViewModelTest {
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@get:Rule
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val mainDispatcherRule = MainDispatcherRule() // see below
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private lateinit var viewModel: CounterViewModel
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@Before
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fun setup() {
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viewModel = CounterViewModel()
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}
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@Test
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fun `increment updates count`() = runTest {
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viewModel.increment()
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assertEquals(1, viewModel.uiState.value.count)
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}
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}
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```
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### Testing Coroutines (Critical)
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The Main dispatcher doesn't exist on the JVM. Replace it with `TestDispatcher` or tests crash with `IllegalStateException`.
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```kotlin
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// Reusable rule — put in a shared test-util module
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class MainDispatcherRule(
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private val dispatcher: TestDispatcher = UnconfinedTestDispatcher()
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) : TestWatcher() {
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override fun starting(description: Description) {
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Dispatchers.setMain(dispatcher)
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}
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override fun finished(description: Description) {
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Dispatchers.resetMain()
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}
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}
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```
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```kotlin
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// ❌ Wrong: No Main dispatcher replacement → crash
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@Test
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fun `load data`() = runTest {
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val vm = MyViewModel(repo)
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vm.load() // launches on Dispatchers.Main → IllegalStateException
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}
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// ✅ Correct: Use MainDispatcherRule
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@get:Rule
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val mainDispatcherRule = MainDispatcherRule()
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@Test
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fun `load data`() = runTest {
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val vm = MyViewModel(repo)
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vm.load()
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assertEquals(UiState.Success, vm.uiState.value)
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}
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```
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### Testing StateFlow with Turbine
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```kotlin
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@Test
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fun `loading then success states`() = runTest {
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val vm = MyViewModel(fakeRepo)
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vm.uiState.test { // Turbine extension
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assertEquals(UiState.Idle, awaitItem())
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vm.load()
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assertEquals(UiState.Loading, awaitItem())
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assertEquals(UiState.Success(data), awaitItem())
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cancelAndIgnoreRemainingEvents()
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}
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}
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```
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### Mocking with MockK
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```kotlin
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@Test
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fun `repository calls api and caches`() = runTest {
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val api = mockk<UserApi>()
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coEvery { api.getUser("42") } returns User("42", "Alice")
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val repo = UserRepository(api)
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val user = repo.getUser("42")
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assertEquals("Alice", user.name)
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coVerify(exactly = 1) { api.getUser("42") }
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}
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```
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| MockK Function | Purpose |
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|----------------|------------------------|
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| `mockk<T>()` | Create mock instance |
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| `every { }` | Stub synchronous calls |
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| `coEvery { }` | Stub suspend functions |
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| `verify { }` | Verify call happened |
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| `coVerify { }` | Verify suspend call |
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| `slot<T>()` | Capture argument value |
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### Robolectric — When You Need Android Classes
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Robolectric simulates the Android framework on the JVM, so tests stay fast while accessing `Context`, `SharedPreferences`, resources, etc.
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```kotlin
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@RunWith(RobolectricTestRunner::class)
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@Config(sdk = [34])
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class PreferencesManagerTest {
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private lateinit var context: Context
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@Before
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fun setup() {
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context = ApplicationProvider.getApplicationContext()
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}
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@Test
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fun `saves and reads theme preference`() {
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val prefs = PreferencesManager(context)
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prefs.setDarkMode(true)
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assertTrue(prefs.isDarkMode())
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}
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}
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```
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### Common Local Test Mistakes
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```kotlin
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// ❌ Wrong: Testing implementation details (fragile)
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@Test
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fun `check internal cache map size`() {
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repo.load()
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assertEquals(1, repo.cacheMap.size) // breaks if cache strategy changes
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}
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// ✅ Correct: Test observable behavior
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@Test
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fun `second call returns cached result without network`() = runTest {
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coEvery { api.fetch() } returns data
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repo.load()
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repo.load()
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coVerify(exactly = 1) { api.fetch() } // only one network call
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}
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```
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---
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## 2. Instrumentation Tests (Espresso)
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Instrumentation tests live in `src/androidTest/` and run on a real device or emulator. Slower than local tests, but they exercise the actual Android stack — use them for UI flows, database integration, and cross-component interaction.
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### Test Runner Setup
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In `app/build.gradle.kts`:
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```kotlin
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android {
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defaultConfig {
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testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
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}
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}
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```
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### Espresso Basics
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Espresso's API follows a consistent pattern: **find → act → assert**.
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```kotlin
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@RunWith(AndroidJUnit4::class)
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class LoginScreenTest {
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@get:Rule
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val activityRule = ActivityScenarioRule(LoginActivity::class.java)
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@Test
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fun validLogin_navigatesToHome() {
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// Find and act
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onView(withId(R.id.email_input))
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.perform(typeText("user@example.com"), closeSoftKeyboard())
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onView(withId(R.id.password_input))
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.perform(typeText("secret123"), closeSoftKeyboard())
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onView(withId(R.id.login_button))
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.perform(click())
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// Assert
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onView(withId(R.id.home_container))
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.check(matches(isDisplayed()))
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}
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}
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```
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| Category | Common Matchers / Actions |
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|------------|------------------------------------------------------------------------------------|
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| **Find** | `withId(R.id.x)`, `withText("x")`, `withContentDescription("x")`, `withHint("x")` |
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| **Act** | `click()`, `typeText("x")`, `clearText()`, `scrollTo()`, `swipeUp()` |
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| **Assert** | `isDisplayed()`, `withText("x")`, `isEnabled()`, `isChecked()`, `doesNotExist()` |
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### Testing Intents
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Espresso-Intents lets you verify outgoing Intents and stub responses (e.g., camera, file picker).
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```kotlin
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@get:Rule
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val intentsRule = IntentsRule()
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@Test
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fun shareButton_launchesShareIntent() {
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onView(withId(R.id.share_button)).perform(click())
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intended(allOf(
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hasAction(Intent.ACTION_SEND),
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hasType("text/plain")
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))
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}
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@Test
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fun cameraButton_handlesResult() {
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val resultData = Intent().apply { putExtra("photo_uri", "content://mock") }
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intending(hasAction(MediaStore.ACTION_IMAGE_CAPTURE))
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.respondWith(Instrumentation.ActivityResult(RESULT_OK, resultData))
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onView(withId(R.id.camera_button)).perform(click())
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onView(withId(R.id.photo_preview)).check(matches(isDisplayed()))
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}
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```
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### IdlingResource for Async Operations
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Espresso waits for the UI thread and AsyncTask by default, but not for custom async work (Retrofit, coroutines, etc.). `IdlingResource` tells Espresso when your app is busy.
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```kotlin
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// In production code (thin wrapper)
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object NetworkIdlingResource {
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private val counter = CountingIdlingResource("Network")
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fun increment() = counter.increment()
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fun decrement() = counter.decrement()
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fun get(): IdlingResource = counter
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}
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// In test setup
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@Before
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fun registerIdling() {
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IdlingRegistry.getInstance().register(NetworkIdlingResource.get())
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}
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@After
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fun unregisterIdling() {
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IdlingRegistry.getInstance().unregister(NetworkIdlingResource.get())
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}
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```
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---
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## 3. UI Automator (Cross-App & System UI)
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UI Automator can interact with any visible UI — system dialogs, notifications, other apps. Use it when Espresso can't reach outside your app's process.
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| Use Case | Why UI Automator |
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|------------------------------|----------------------------------------|
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| Runtime permission dialogs | System UI, outside app process |
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| Notification actions | System notification shade |
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| Device settings interaction | Settings app |
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| Multi-app workflows | e.g., share to another app and return |
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```kotlin
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@RunWith(AndroidJUnit4::class)
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class PermissionFlowTest {
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private lateinit var device: UiDevice
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@Before
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fun setup() {
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device = UiDevice.getInstance(InstrumentationRegistry.getInstrumentation())
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}
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@Test
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fun grantsCameraPermission_andOpensCamera() {
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// Trigger permission request from within your app
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onView(withId(R.id.camera_button)).perform(click())
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// Handle the system permission dialog via UI Automator
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val allowButton = device.findObject(
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By.res("com.android.permissioncontroller:id/permission_allow_foreground_only_button")
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)
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allowButton?.click()
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// Back in Espresso territory — verify the camera view appeared
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onView(withId(R.id.camera_preview)).check(matches(isDisplayed()))
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}
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@Test
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fun notificationTap_opensDetail() {
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// Open notification shade
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device.openNotification()
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device.wait(Until.hasObject(By.textStartsWith("New message")), 5000)
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// Tap the notification
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val notification = device.findObject(By.textStartsWith("New message"))
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notification.click()
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// Verify deep-link target
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onView(withId(R.id.message_detail)).check(matches(isDisplayed()))
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}
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}
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```
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---
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## 4. Compose UI Testing
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Compose has its own testing framework that works with the semantic tree rather than the view hierarchy. Tests can run as local tests (with Robolectric) or instrumentation tests — the API is the same.
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### Basic Setup
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```kotlin
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@RunWith(AndroidJUnit4::class)
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class GreetingScreenTest {
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@get:Rule
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val composeTestRule = createComposeRule()
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@Test
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fun displaysGreeting_andRespondsToClick() {
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composeTestRule.setContent {
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MyAppTheme {
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GreetingScreen(name = "World")
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}
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}
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composeTestRule.onNodeWithText("Hello, World!")
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.assertIsDisplayed()
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composeTestRule.onNodeWithText("Say Hi")
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.performClick()
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composeTestRule.onNodeWithText("Hi back!")
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.assertIsDisplayed()
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}
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}
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```
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### Finders, Assertions & Actions
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| Category | API | Example |
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|------------|----------------------------------------------|---------------------------------|
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| **Find** | `onNodeWithText("x")` | Matches visible text |
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| | `onNodeWithTag("x")` | Matches `Modifier.testTag("x")` |
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| | `onNodeWithContentDescription("x")` | Matches semantics label |
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| | `onAllNodesWithTag("x")` | Returns list of matches |
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| **Assert** | `assertIsDisplayed()` | Node is visible |
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| | `assertTextEquals("x")` | Exact text match |
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| | `assertIsEnabled()` / `assertIsNotEnabled()` | Enabled state |
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| | `assertDoesNotExist()` | Node not in tree |
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| | `assertCountEquals(n)` | For `onAllNodes` |
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| **Act** | `performClick()` | Tap |
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| | `performTextInput("x")` | Type into text field |
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| | `performScrollTo()` | Scroll node into view |
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| | `performTouchInput { swipeUp() }` | Gestures |
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### Using testTag for Reliable Selectors
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Text-based finders break with localization or copy changes. Use `testTag` for stable selectors:
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```kotlin
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// ❌ Fragile: breaks if text changes or app is localized
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composeTestRule.onNodeWithText("Submit Order").performClick()
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// ✅ Stable: testTag doesn't change with locale
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composeTestRule.onNodeWithTag("submit_order_button").performClick()
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```
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```kotlin
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// In production Composable
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Button(
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onClick = { /* ... */ },
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modifier = Modifier.testTag("submit_order_button")
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) {
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Text(stringResource(R.string.submit_order))
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}
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```
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### Testing with Activity Context
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When your Composable needs a `ComponentActivity` (e.g., for `viewModel()` or navigation), use `createAndroidComposeRule`:
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```kotlin
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@get:Rule
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val composeTestRule = createAndroidComposeRule<MainActivity>()
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@Test
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fun fullScreen_endToEnd() {
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// Activity is already launched — interact with the real content
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composeTestRule.onNodeWithTag("login_email")
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.performTextInput("user@test.com")
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composeTestRule.onNodeWithTag("login_password")
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.performTextInput("pass123")
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composeTestRule.onNodeWithTag("login_submit")
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.performClick()
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composeTestRule.waitUntil(timeoutMillis = 5000) {
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composeTestRule.onAllNodesWithTag("home_screen")
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.fetchSemanticsNodes().isNotEmpty()
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}
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composeTestRule.onNodeWithTag("home_screen")
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.assertIsDisplayed()
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}
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```
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### Testing Navigation
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```kotlin
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@Test
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fun navigatesToDetail_onItemClick() {
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val navController = TestNavHostController(ApplicationProvider.getApplicationContext())
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composeTestRule.setContent {
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navController.navigatorProvider.addNavigator(ComposeNavigator())
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MyAppNavHost(navController = navController)
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}
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// Click item on list screen
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composeTestRule.onNodeWithTag("item_0").performClick()
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// Verify navigation destination
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assertEquals("detail/0", navController.currentBackStackEntry?.destination?.route)
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}
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```
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### Common Compose Test Mistakes
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```kotlin
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// ❌ Wrong: Asserting immediately after async operation
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composeTestRule.onNodeWithTag("submit").performClick()
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composeTestRule.onNodeWithText("Success").assertIsDisplayed() // may fail — UI hasn't updated yet
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// ✅ Correct: Wait for the UI to settle
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composeTestRule.onNodeWithTag("submit").performClick()
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composeTestRule.waitForIdle()
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composeTestRule.onNodeWithText("Success").assertIsDisplayed()
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// ✅ Also correct: waitUntil for longer async work
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composeTestRule.onNodeWithTag("submit").performClick()
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composeTestRule.waitUntil(timeoutMillis = 3000) {
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composeTestRule.onAllNodesWithText("Success")
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.fetchSemanticsNodes().isNotEmpty()
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}
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```
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---
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## 5. Gradle Managed Devices
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||||
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||||
Define emulator profiles in `build.gradle.kts` so anyone (including CI) can run instrumentation tests without manually creating AVDs. Gradle downloads the system image, creates the emulator, runs tests, and tears it down automatically.
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### Device Configuration
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||||
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||||
In `app/build.gradle.kts`:
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||||
```kotlin
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||||
android {
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testOptions {
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managedDevices {
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localDevices {
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create("pixel6Api34") {
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device = "Pixel 6"
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||||
apiLevel = 34
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systemImageSource = "aosp-atd" // ATD = faster, headless
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}
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create("pixel4Api30") {
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device = "Pixel 4"
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||||
apiLevel = 30
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||||
systemImageSource = "aosp-atd"
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}
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create("smallTabletApi34") {
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||||
device = "Nexus 7"
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||||
apiLevel = 34
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||||
systemImageSource = "google" // full Google APIs image
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||||
}
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||||
}
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||||
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||||
// Group devices for matrix testing
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||||
groups {
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||||
create("phoneTests") {
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||||
targetDevices.add(devices["pixel6Api34"])
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||||
targetDevices.add(devices["pixel4Api30"])
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||||
}
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||||
create("allDevices") {
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||||
targetDevices.add(devices["pixel6Api34"])
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||||
targetDevices.add(devices["pixel4Api30"])
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||||
targetDevices.add(devices["smallTabletApi34"])
|
||||
}
|
||||
}
|
||||
}
|
||||
}
|
||||
}
|
||||
```
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||||
|
||||
### System Image Sources
|
||||
|
||||
| Source | Description | Best For |
|
||||
|----------------|---------------------------------------------------|------------------------------|
|
||||
| `"aosp-atd"` | Automated Test Device — minimal, no Play Services | Fast CI, pure logic tests |
|
||||
| `"google-atd"` | ATD with Google APIs | Tests needing Maps, Firebase |
|
||||
| `"aosp"` | Full AOSP image | Standard emulator testing |
|
||||
| `"google"` | Full image with Google Play Services | Play Services integration |
|
||||
|
||||
ATD images boot faster and consume less memory because they strip out UI chrome and preinstalled apps irrelevant to testing. Prefer `aosp-atd` or `google-atd` for CI pipelines.
|
||||
|
||||
### Running Tests
|
||||
|
||||
```bash
|
||||
# Run on a single managed device
|
||||
./gradlew pixel6Api34DebugAndroidTest
|
||||
|
||||
# Run on a device group (all devices in parallel if hardware allows)
|
||||
./gradlew phoneTestsGroupDebugAndroidTest
|
||||
./gradlew allDevicesGroupDebugAndroidTest
|
||||
|
||||
# With specific flavor
|
||||
./gradlew pixel6Api34DevDebugAndroidTest
|
||||
|
||||
# Enable test sharding across devices (speeds up large suites)
|
||||
./gradlew allDevicesGroupDebugAndroidTest \
|
||||
-Pandroid.experimental.androidTest.numManagedDeviceShards=2
|
||||
|
||||
# Generate HTML test report
|
||||
./gradlew pixel6Api34DebugAndroidTest \
|
||||
--continue # don't stop on first failure
|
||||
```
|
||||
|
||||
Test results are written to `app/build/reports/androidTests/managedDevice/`.
|
||||
Reference in New Issue
Block a user