unit-testing

# Kotlin Unit Testing Guidelines & Best Practices for Flow This skill outlines the standards and conventions for writing unit tests in the Flow codebase (`io.github.aedev.flow`). ## 1. Naming Conventions ### Test Class Naming - Test class names MUST mirror the target class with a `Test` suffix. - Example: `LikedVideosViewModel` → `LikedVideosViewModelTest` - Example: `HistoryViewModel` → `HistoryViewModelTest` - Example: `SearchViewModel` → `SearchViewModelTest` ### Test Method Naming - Use backtick-quoted descriptive phrases outlining the scenario and expected outcome: - Format: `` `[given condition or action] [expected result]` `` - Good: `` `initial state loads liked videos from repository` `` - Good: `` `removeLike calls repository and updates state` `` - Good: `` `search with query updates results flow` `` - Bad: `testRemoveLike()`, `test1()` --- ## 2. Mocking Framework & Cleanup Rules - **Framework**: Use **MockK** (`io.mockk.*`). - **Initialization**: Create mocks in `@Before` or as class properties via `mockk(relaxed = true)` or `mockk()`. - **Teardown / Cleanup**: ALWAYS clean up mocks in an `@After` method using `unmockkAll()` or `clearAllMocks()` to ensure isolated test execution and prevent memory leaks/polluted mock states across tests. ```kotlin @Before fun setUp() { repository = mockk(relaxed = true) } @After fun tearDown() { unmockkAll() } ``` --- ## 3. Coroutines & ViewModel Testing ViewModel unit tests run on the JVM without an Android Main Looper. Since `viewModelScope` uses `Dispatchers.Main`, you MUST replace the Main dispatcher during tests: - Use `Dispatchers.setMain(testDispatcher)` in `@Before` (or via a JUnit `TestRule`). - Use `Dispatchers.resetMain()` in `@After`. - Wrap suspend test logic inside `runTest` from `kotlinx.coroutines.test`. ```kotlin @OptIn(ExperimentalCoroutinesApi::class) class MyViewModelTest { private val testDispatcher = StandardTestDispatcher() @Before fun setUp() { Dispatchers.setMain(testDispatcher) } @After fun tearDown() { Dispatchers.resetMain() unmockkAll() } } ``` --- ## 4. Assertions & AAA Pattern - **Assertion Library**: Use **Google Truth** (`com.google.common.truth.Truth.assertThat`). - **AAA Pattern**: Structure tests clearly with **Arrange**, **Act**, and **Assert**: ```kotlin @Test fun `removeLike calls repository to remove item`() = runTest { // Arrange val videoId = "test_id_123" coEvery { repository.removeLikeState(videoId) } returns Unit // Act viewModel.removeLike(videoId) testScheduler.advanceUntilIdle() // Assert coVerify(exactly = 1) { repository.removeLikeState(videoId) } } ``` --- ## 5. Summary Checklist Before Shipping Tests 1. ✅ Test file resides under `app/src/test/java/...` matching package structure of source class. 2. ✅ Method names use backtick-quoted descriptive sentences. 3. ✅ MockK is used for dependencies with `unmockkAll()` in `@After`. 4. ✅ Main dispatcher rule/setup is present for ViewModel tests. 5. ✅ Google Truth (`assertThat`) is used for assertions. 6. ✅ Test passes cleanly via `./gradlew :app:testGithubDebugUnitTest`.