testImplementation("junit:junit:$junitVerison")
    testImplementation("org.jetbrains.kotlinx:kotlinx-coroutines-test:$coroutineTestVersion")
    testImplementation("app.cash.turbine:turbine:$turbineVersion")

class FakeTodoRepository : TodoRepository {
    
    // 내부적으로 데이터를 보관
    private val todos = MutableStateFlow(listOf<TodoItem>())
    
    // 반환할 때 Flow로 타입으로 반환
    override fun getTodos(): Flow<List<TodoItem>> = todos

    override suspend fun setTodo(todoItem: TodoItem) {
        todos.emit(todos.value.map { item -> if (item.id == todoItem.id) todoItem else item })
    }

    // ...
}

    // Create an empty collector for the StateFlow
    backgroundScope.launch(UnconfinedTestDispatcher(testScheduler)) {
        viewModel.score.collect()
    }

public fun runTest(
    context: CoroutineContext = EmptyCoroutineContext,
    timeout: Duration = DEFAULT_TIMEOUT,
    testBody: suspend TestScope.() -> Unit
): TestResult {
    check(context[RunningInRunTest] == null) {
        "Calls to `runTest` can't be nested. Please read the docs on `TestResult` for details."
    }
    return TestScope(context + RunningInRunTest).runTest(timeout, testBody)
}

// ...
    @Test
    @OptIn(ExperimentalCoroutinesApi::class)
    fun `랜덤 사진을 눌렀을 때 랜덤하게 사진 URL이 받아와 지는지`() = runTest {
        backgroundScope.launch(UnconfinedTestDispatcher(testScheduler)) {
            editViewModel.userPhoto.collect()
        }

        // When
        editViewModel.setRandomPhoto()

        // Then
        assertEquals(FakePhotoRepository.RANDOM_URL, editViewModel.userPhoto.value)
    }
// ...

    // EditViewModel.kt
    val userPhoto = userRepository.userPhotoUrlFlow.stateIn(
        scope = viewModelScope, // Dispatcher.Main.immediate 사용
        started = SharingStarted.WhileSubscribed(SUBSCRIPTION_TIMEOUT),
        initialValue = null,
    )

// 테스트 룰
@OptIn(ExperimentalCoroutinesApi::class)
class MainDispatcherRule(
    private val testDispatcher: TestDispatcher = UnconfinedTestDispatcher(),
) : TestWatcher() {
    override fun starting(description: Description) {
        Dispatchers.setMain(testDispatcher)
    }

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

// 테스트 코드
class EditViewModelTest {
    @get:Rule
    val mainDispatcherRule = MainDispatcherRule() 
    // ...
}

// 기존 테스트 코드
class EditViewModelTest {

    @get:Rule
    val mainDispatcherRule = MainDispatcherRule()

    private lateinit var fakeUserRepository: UserRepository
    private lateinit var fakePhotoRepository: PhotoRepository // 테스트에 사용되지 않을 객체
    private lateinit var setRandomPhotoUseCase: SetRandomPhotoUseCase // 테스트에 사용되지 않을 객체
    private lateinit var editViewModel: EditViewModel

    // 테스트에 직적적인 연관이 없는 사전 로직
    @Before
    fun setUp() {
        fakeUserRepository = FakeUserRepository()
        fakePhotoRepository = FakePhotoRepository()
        setRandomPhotoUseCase = SetRandomPhotoUseCase(fakePhotoRepository, fakeUserRepository)
        editViewModel = EditViewModel(
            fakeUserRepository,
            setRandomPhotoUseCase,
        )
    }
        
    @Test
    fun test1() {
        // ... 
    }
}

// 책임 분리 리펙토링 테스트 코드
class EditViewModelTest {

    @get:Rule
    val editViewModelTestRule = EditViewModelTestRule()

    @Test
    fun test1() = with(editViewModelTestRule){
        // ... 
    }
}

// 테스트 룰
// MainDispatcherRule을 상속해서 기존 동작(setMain)을 유지
class EditViewModelTestRule : MainDispatcherRule() {
    
    lateinit var editViewModel: EditViewModel               // 테스트코드에 공개 시킬 객체 
    lateinit var fakeUserRepository: FakeUserRepository     // 테스트코드에 공개 시킬 객체 
    
    override fun starting(description: Description) {
        super.starting(description)

        val fakePhotoRepository = FakePhotoRepository()
        fakeUserRepository = FakeUserRepository()
        val setRandomPhotoUseCase = SetRandomPhotoUseCase(fakePhotoRepository, fakeUserRepository)
        editViewModel = EditViewModel(
            fakeUserRepository,
            setRandomPhotoUseCase,
        )
    }
}