Testing trong Android

1. Giới thiệu

Testing đảm bảo code hoạt động đúng và giúp refactor an toàn.

2. Testing Pyramid

        ┌─────────────┐
        │  E2E/UI     │  ← Slow, expensive
        ├─────────────┤
        │ Integration │
        ├─────────────┤
        │  Unit Tests │  ← Fast, cheap
        └─────────────┘

3. Setup

build.gradle.kts

dependencies {
    // Unit tests
    testImplementation("junit:junit:4.13.2")
    testImplementation("org.jetbrains.kotlinx:kotlinx-coroutines-test:1.8.0")
    testImplementation("io.mockk:mockk:1.13.10")

    // Android/Instrumentation tests
    androidTestImplementation("androidx.test.ext:junit:1.1.5")
    androidTestImplementation("androidx.test.espresso:espresso-core:3.5.1")
    androidTestImplementation("androidx.compose.ui:ui-test-junit4")
}

4. Unit Tests

Test ViewModel

class UserViewModelTest {

    @get:Rule
    val mainDispatcherRule = MainDispatcherRule()

    private lateinit var repository: UserRepository
    private lateinit var viewModel: UserViewModel

    @Before
    fun setup() {
        repository = mockk()
        viewModel = UserViewModel(repository)
    }

    @Test
    fun `loadUsers success updates state`() = runTest {
        // Given
        val users = listOf(User(1, "Alice", "alice@email.com"))
        coEvery { repository.getUsers() } returns Result.success(users)

        // When
        viewModel.loadUsers()

        // Then
        assertEquals(users, viewModel.uiState.value.users)
        assertEquals(false, viewModel.uiState.value.isLoading)
    }

    @Test
    fun `loadUsers error shows error message`() = runTest {
        // Given
        coEvery { repository.getUsers() } returns Result.failure(Exception("Network error"))

        // When
        viewModel.loadUsers()

        // Then
        assertEquals("Network error", viewModel.uiState.value.error)
    }
}

// MainDispatcherRule for testing
class MainDispatcherRule : TestWatcher() {
    val dispatcher = StandardTestDispatcher()

    override fun starting(description: Description) {
        Dispatchers.setMain(dispatcher)
    }

    override fun finished(description: Description) {
        Dispatchers.resetMain()
    }
}

Test UseCase

class GetUsersUseCaseTest {

    private val repository: UserRepository = mockk()
    private val useCase = GetUsersUseCase(repository)

    @Test
    fun `invoke returns users from repository`() = runTest {
        val expected = listOf(User(1, "Alice"))
        coEvery { repository.getUsers() } returns Result.success(expected)

        val result = useCase()

        assertTrue(result.isSuccess)
        assertEquals(expected, result.getOrNull())
    }
}

5. Compose UI Tests

class UserListScreenTest {

    @get:Rule
    val composeTestRule = createComposeRule()

    @Test
    fun displayUserList() {
        val users = listOf(
            User(1, "Alice", "alice@email.com"),
            User(2, "Bob", "bob@email.com")
        )

        composeTestRule.setContent {
            UserListContent(users = users, onUserClick = {})
        }

        composeTestRule.onNodeWithText("Alice").assertExists()
        composeTestRule.onNodeWithText("Bob").assertExists()
    }

    @Test
    fun clickUser_triggersCallback() {
        var clickedId: Int? = null

        composeTestRule.setContent {
            UserListContent(
                users = listOf(User(1, "Alice")),
                onUserClick = { clickedId = it }
            )
        }

        composeTestRule.onNodeWithText("Alice").performClick()
        assertEquals(1, clickedId)
    }

    @Test
    fun searchField_filtersUsers() {
        composeTestRule.setContent {
            UserSearchScreen()
        }

        composeTestRule.onNodeWithTag("search_field")
            .performTextInput("alice")

        composeTestRule.onNodeWithText("Alice").assertExists()
        composeTestRule.onNodeWithText("Bob").assertDoesNotExist()
    }
}

6. Test Finders

// By text
onNodeWithText("Hello")
onAllNodesWithText("Item")

// By content description
onNodeWithContentDescription("Back")

// By testTag
onNodeWithTag("button_submit")

// By semantic properties
onNode(hasText("Hello") and hasClickAction())

// All nodes
onAllNodes(hasText("Item")).assertCountEquals(5)

7. Test Actions

// Click
onNodeWithText("Submit").performClick()

// Type text
onNodeWithTag("input").performTextInput("Hello")
onNodeWithTag("input").performTextClearance()

// Scroll
onNodeWithTag("list").performScrollToIndex(10)

// Swipe
onNodeWithTag("card").performTouchInput {
    swipeLeft()
}

8. Test Assertions

onNodeWithText("Hello").assertExists()
onNodeWithText("Hello").assertDoesNotExist()
onNodeWithTag("button").assertIsEnabled()
onNodeWithTag("button").assertIsNotEnabled()
onNodeWithTag("checkbox").assertIsSelected()
onNodeWithText("Title").assertIsDisplayed()

9. Testing với Hilt

@HiltAndroidTest
class UserScreenTest {

    @get:Rule(order = 0)
    val hiltRule = HiltAndroidRule(this)

    @get:Rule(order = 1)
    val composeTestRule = createAndroidComposeRule<MainActivity>()

    @Inject
    lateinit var repository: UserRepository

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

    @Test
    fun userScreenLoadsData() {
        composeTestRule.onNodeWithTag("user_list").assertExists()
    }
}

// Fake module for testing
@Module
@TestInstallIn(
    components = [SingletonComponent::class],
    replaces = [RepositoryModule::class]
)
object FakeRepositoryModule {
    @Provides
    @Singleton
    fun provideFakeRepository(): UserRepository = FakeUserRepository()
}

10. Testing StateFlow

@Test
fun testStateFlow() = runTest {
    val viewModel = UserViewModel(fakeRepository)

    viewModel.uiState.test {
        assertEquals(UiState.Loading, awaitItem())

        viewModel.loadUsers()

        val successState = awaitItem()
        assertTrue(successState is UiState.Success)
    }
}

11. Screenshot Testing

@Test
fun userCard_matchesScreenshot() {
    composeTestRule.setContent {
        UserCard(user = User(1, "Alice", "alice@email.com"))
    }

    composeTestRule.onNodeWithTag("user_card")
        .captureToImage()
        .assertAgainstGolden(rule, "user_card")
}

---

📝 Tóm tắt

Test Type	Location	Speed
Unit	src/test	Fast
Integration	src/test or src/androidTest	Medium
UI/Compose	src/androidTest	Slow

Framework	Purpose
JUnit	Test runner
MockK	Mocking
Turbine	Flow testing
Compose Test	UI testing