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Overview

A solid testing strategy is essential for building reliable Android applications. This guide covers testing approaches inspired by Google’s “Now in Android” sample, including unit tests, Hilt integration tests, and screenshot testing with Roborazzi.

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Testing Pyramid

Follow the testing pyramid for an effective test suite: 
        /\
       /  \    UI/Screenshot Tests
      /    \   (Few, slow, high-level)
     /------\
    /        \  Integration Tests
   /          \ (Some, medium speed)
  /------------\
 /              \ Unit Tests
/________________\ (Many, fast, focused)
  1. Unit Tests: Fast, isolated tests for business logic (ViewModels, Repositories, Use Cases)
  2. Integration Tests: Test component interactions (Room DAOs with database, Retrofit with MockWebServer)
  3. UI/Screenshot Tests: Verify UI correctness and prevent visual regressions (Compose UI)

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Dependencies Setup

Add these testing dependencies to your libs.versions.toml: 
[versions]
kotlinxCoroutines = "1.7.3"
hilt = "2.48"
roborazzi = "1.7.0"

[libraries]
# Unit testing
junit4 = { module = "junit:junit", version = "4.13.2" }
kotlinx-coroutines-test = { group = "org.jetbrains.kotlinx", name = "kotlinx-coroutines-test", version.ref = "kotlinxCoroutines" }

# Android testing
androidx-test-ext-junit = { group = "androidx.test.ext", name = "junit", version = "1.1.5" }
espresso-core = { group = "androidx.test.espresso", name = "espresso-core", version = "3.5.1" }
compose-ui-test = { group = "androidx.compose.ui", name = "ui-test-junit4" }

# Hilt testing
hilt-android-testing = { group = "com.google.dagger", name = "hilt-android-testing", version.ref = "hilt" }

# Screenshot testing
roborazzi = { group = "io.github.takahirom.roborazzi", name = "roborazzi", version.ref = "roborazzi" }

[plugins]
roborazzi = { id = "io.github.takahirom.roborazzi", version.ref = "roborazzi" }
In your module’s build.gradle.kts: 
dependencies {
    // Unit tests
    testImplementation(libs.junit4)
    testImplementation(libs.kotlinx.coroutines.test)
    
    // Android instrumented tests
    androidTestImplementation(libs.androidx.test.ext.junit)
    androidTestImplementation(libs.espresso.core)
    androidTestImplementation(libs.compose.ui.test)
    
    // Hilt testing
    androidTestImplementation(libs.hilt.android.testing)
    kaptAndroidTest(libs.hilt.android.compiler)
    
    // Screenshot testing
    testImplementation(libs.roborazzi)
}

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Unit Testing

Unit tests are fast, focused tests that verify individual components in isolation.

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Testing ViewModels

class ArticleViewModelTest {
    
    @get:Rule
    val dispatcherRule = MainDispatcherRule()
    
    private val mockRepository = mockk<ArticleRepository>()
    private lateinit var viewModel: ArticleViewModel
    
    @Before
    fun setup() {
        viewModel = ArticleViewModel(mockRepository)
    }
    
    @Test
    fun `when articles loaded, uiState shows success`() = runTest {
        // Given
        val articles = listOf(
            Article(id = 1, title = "Test Article")
        )
        coEvery { mockRepository.getArticles() } returns flowOf(articles)
        
        // When
        viewModel.loadArticles()
        
        // Then
        val state = viewModel.uiState.value
        assertThat(state).isInstanceOf(UiState.Success::class.java)
        assertThat((state as UiState.Success).data).isEqualTo(articles)
    }
    
    @Test
    fun `when repository throws error, uiState shows error`() = runTest {
        // Given
        coEvery { mockRepository.getArticles() } throws Exception("Network error")
        
        // When
        viewModel.loadArticles()
        
        // Then
        assertThat(viewModel.uiState.value).isInstanceOf(UiState.Error::class.java)
    }
}

​
Testing Use Cases

class GetUserPreferencesUseCaseTest {
    
    private val mockDataStore = mockk<PreferencesDataStore>()
    private lateinit var useCase: GetUserPreferencesUseCase
    
    @Before
    fun setup() {
        useCase = GetUserPreferencesUseCase(mockDataStore)
    }
    
    @Test
    fun `returns user preferences from data store`() = runTest {
        // Given
        val expected = UserPreferences(theme = Theme.DARK)
        every { mockDataStore.userPreferences } returns flowOf(expected)
        
        // When
        val result = useCase().first()
        
        // Then
        assertThat(result).isEqualTo(expected)
    }
}

​
Integration Testing

Integration tests verify that multiple components work together correctly.

​
Testing Room DAOs

@HiltAndroidTest
class ArticleDaoTest {
    
    @get:Rule
    var hiltRule = HiltAndroidRule(this)
    
    @Inject
    lateinit var database: AppDatabase
    private lateinit var articleDao: ArticleDao
    
    @Before
    fun init() {
        hiltRule.inject()
        articleDao = database.articleDao()
    }
    
    @After
    fun cleanup() {
        database.close()
    }
    
    @Test
    fun insertAndRetrieveArticle() = runTest {
        // Given
        val article = ArticleEntity(
            id = 1,
            title = "Test Article",
            content = "Test content"
        )
        
        // When
        articleDao.insert(article)
        val retrieved = articleDao.getArticleById(1).first()
        
        // Then
        assertThat(retrieved).isEqualTo(article)
    }
    
    @Test
    fun deleteArticle() = runTest {
        // Given
        val article = ArticleEntity(id = 1, title = "Test")
        articleDao.insert(article)
        
        // When
        articleDao.delete(article)
        val result = articleDao.getArticleById(1).first()
        
        // Then
        assertThat(result).isNull()
    }
}

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Testing with MockWebServer

class ArticleApiTest {
    
    private lateinit var mockWebServer: MockWebServer
    private lateinit var api: ArticleApi
    
    @Before
    fun setup() {
        mockWebServer = MockWebServer()
        mockWebServer.start()
        
        val retrofit = Retrofit.Builder()
            .baseUrl(mockWebServer.url("/"))
            .addConverterFactory(GsonConverterFactory.create())
            .build()
            
        api = retrofit.create(ArticleApi::class.java)
    }
    
    @After
    fun teardown() {
        mockWebServer.shutdown()
    }
    
    @Test
    fun `fetch articles returns list`() = runTest {
        // Given
        val response = """
            {
                "articles": [
                    {"id": 1, "title": "Article 1"},
                    {"id": 2, "title": "Article 2"}
                ]
            }
        """.trimIndent()
        
        mockWebServer.enqueue(
            MockResponse()
                .setResponseCode(200)
                .setBody(response)
        )
        
        // When
        val result = api.getArticles()
        
        // Then
        assertThat(result.articles).hasSize(2)
        assertThat(result.articles[0].title).isEqualTo("Article 1")
    }
}

​
Hilt Testing

Hilt provides HiltAndroidRule and @HiltAndroidTest for dependency injection in tests.
1

Add Hilt test dependency

androidTestImplementation(libs.hilt.android.testing)
kaptAndroidTest(libs.hilt.android.compiler)
2

Annotate test class

@HiltAndroidTest
class MyFeatureTest {
    @get:Rule
    var hiltRule = HiltAndroidRule(this)
    
    // Test code
}
3

Inject dependencies

@Inject
lateinit var repository: ArticleRepository

@Before
fun init() {
    hiltRule.inject()
}

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Replacing Modules in Tests

@Module
@InstallIn(SingletonComponent::class)
object TestDatabaseModule {
    
    @Provides
    @Singleton
    fun provideInMemoryDatabase(
        @ApplicationContext context: Context
    ): AppDatabase = Room.inMemoryDatabaseBuilder(
        context,
        AppDatabase::class.java
    ).allowMainThreadQueries().build()
}

@HiltAndroidTest
@UninstallModules(DatabaseModule::class) // Replace production module
class ArticleFeatureTest {
    // Uses in-memory database instead of production database
}

​
Screenshot Testing with Roborazzi

Screenshot tests ensure your UI doesn’t regress visually. Roborazzi runs on the JVM (fast) without needing an emulator or device.
1

Add Roborazzi plugin

In libs.versions.toml:
[versions]
roborazzi = "1.7.0"

[plugins]
roborazzi = { id = "io.github.takahirom.roborazzi", version.ref = "roborazzi" }
2

Apply plugin to module

In your module’s build.gradle.kts:
plugins {
    alias(libs.plugins.roborazzi)
}
3

Add test dependency

dependencies {
    testImplementation(libs.roborazzi)
}

​
Writing Screenshot Tests

@RunWith(AndroidJUnit4::class)
@GraphicsMode(GraphicsMode.Mode.NATIVE)
@Config(sdk = [33], qualifiers = RobolectricDeviceQualifiers.Pixel5)
class ArticleScreenScreenshotTest {
    
    @get:Rule
    val composeTestRule = createAndroidComposeRule<ComponentActivity>()
    
    @Test
    fun articleScreen_loading() {
        composeTestRule.setContent {
            AppTheme {
                ArticleScreen(
                    uiState = ArticleUiState.Loading
                )
            }
        }
        
        composeTestRule.onRoot()
            .captureRoboImage("article_screen_loading.png")
    }
    
    @Test
    fun articleScreen_success() {
        composeTestRule.setContent {
            AppTheme {
                ArticleScreen(
                    uiState = ArticleUiState.Success(
                        articles = listOf(
                            Article(id = 1, title = "Test Article")
                        )
                    )
                )
            }
        }
        
        composeTestRule.onRoot()
            .captureRoboImage("article_screen_success.png")
    }
    
    @Test
    fun articleScreen_darkTheme() {
        composeTestRule.setContent {
            AppTheme(darkTheme = true) {
                ArticleScreen(
                    uiState = ArticleUiState.Success(
                        articles = sampleArticles
                    )
                )
            }
        }
        
        composeTestRule.onRoot()
            .captureRoboImage("article_screen_dark.png")
    }
}

​
Testing Individual Composables

@RunWith(AndroidJUnit4::class)
@GraphicsMode(GraphicsMode.Mode.NATIVE)
@Config(sdk = [33])
class ArticleCardScreenshotTest {
    
    @get:Rule
    val composeTestRule = createComposeRule()
    
    @Test
    fun articleCard_default() {
        composeTestRule.setContent {
            AppTheme {
                ArticleCard(
                    article = Article(
                        id = 1,
                        title = "Sample Article",
                        author = "John Doe",
                        publishDate = "2024-01-15"
                    ),
                    onClick = {}
                )
            }
        }
        
        composeTestRule.onNodeWithTag("article_card")
            .captureRoboImage()
    }
}

@Config(
    sdk = [33], // Android SDK version
    qualifiers = RobolectricDeviceQualifiers.Pixel5, // Device config
    application = HiltTestApplication::class // For Hilt
)
@GraphicsMode(GraphicsMode.Mode.NATIVE) // Better rendering
class MyScreenshotTest {
    // Capture with custom options
    composeTestRule.onRoot()
        .captureRoboImage(
            filePath = "screenshots/my_screen.png",
            roborazziOptions = RoborazziOptions(
                compareOptions = CompareOptions(
                    threshold = 0.01 // 1% difference allowed
                ),
                recordOptions = RecordOptions(
                    resizeScale = 0.5 // Half size for faster tests
                )
            )
        )
}

​
Running Tests

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Command Line

# Run all unit tests
./gradlew test

# Run unit tests for specific module
./gradlew :app:testDebugUnitTest

# Run all Android instrumented tests
./gradlew connectedAndroidTest

# Record new screenshots (baseline)
./gradlew recordRoborazziDebug

# Verify screenshots match baseline
./gradlew verifyRoborazziDebug

# Compare and generate diff report
./gradlew compareRoborazziDebug

# Run tests with coverage
./gradlew testDebugUnitTestCoverage

​
Android Studio

1

Run single test

Click the green play button next to the test method or class.
2

Run with coverage

Right-click test > “Run with Coverage” to see code coverage report.
3

View test results

Check the “Run” panel at the bottom for test results and failures.

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Test Best Practices

  • Arrange-Act-Assert: Structure tests clearly with Given-When-Then or Arrange-Act-Assert
  • One assertion per test: Focus each test on a single behavior
  • Descriptive names: Use backticks for readable test names: `when user clicks button, navigate to details`
  • Mock external dependencies: Use MockK or Mockito to isolate the unit under test
  • Test edge cases: Null values, empty lists, error states, etc.
  • Use real implementations: Test actual Room database, real Retrofit setup
  • Clean state: Reset database/server state before each test
  • Test interactions: Verify components work together correctly
  • Reasonable scope: Don’t test the entire app - focus on specific integrations
  • Test multiple states: Loading, success, error, empty states
  • Test themes: Light and dark theme variations
  • Test different configurations: Different screen sizes, font scales, locales
  • Keep tests fast: Use JVM-based Roborazzi instead of instrumented tests
  • Review diffs carefully: Check generated diff images when tests fail
  • Version control baselines: Commit screenshot baselines to git

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Continuous Integration

Integrate tests into your CI pipeline: 
# GitHub Actions example
name: Android CI

on: [push, pull_request]

jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3
      
      - name: Set up JDK 17
        uses: actions/setup-java@v3
        with:
          java-version: '17'
          
      - name: Run unit tests
        run: ./gradlew test
        
      - name: Verify screenshots
        run: ./gradlew verifyRoborazziDebug
        
      - name: Upload test results
        if: failure()
        uses: actions/upload-artifact@v3
        with:
          name: test-results
          path: '**/build/reports/tests/'
          
      - name: Upload screenshot diffs
        if: failure()
        uses: actions/upload-artifact@v3
        with:
          name: roborazzi-diffs
          path: '**/build/outputs/roborazzi/'

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