private const val DEFAULT_TIMEOUT = 500L
@HiltViewModel
class MyViewModel @Inject constructor(
    userRepository: UserRepository
): ViewModel() {
    val userFlow: StateFlow<UiState> = userRepository
        .getUsers()
        .asResult() // 此處返回Flow<Result<User>>
        .map { result ->
            when(result) {
                is Result.Loading -> UiState.Loading
                is Result.Success -> UiState.Success(result.data)
                is Result.Error -> UiState.Error(result.exception)
            }
        }
        .stateIn(
            scope = viewModelScope,
            initialValue = UiState.Loading,
            started = SharingStarted.WhileSubscribed(DEFAULT_TIMEOUT) 
        )
        // started參數(shù)保證了當(dāng)配置改變時(shí)不會(huì)重新觸發(fā)訂閱
}

// 收集StateFlow
val uiState by viewModel.userFlow.collectAsStateWithLifecycle()
// 收集SharedFlow，區(qū)別在于需要賦初始值
val uiState by viewModel.userFlow.collectAsStateWithLifecycle(
    initialValue = UiState.Loading
)
when(uiState) {
    is UiState.Loading -> TODO()
    is UiState.Success -> TODO()
    is UiState.Error -> TODO()
}

import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.test.TestDispatcher
import kotlinx.coroutines.test.UnconfinedTestDispatcher
import kotlinx.coroutines.test.resetMain
import kotlinx.coroutines.test.setMain
import org.junit.rules.TestRule
import org.junit.rules.TestWatcher
import org.junit.runner.Description
/**
 * A JUnit [TestRule] that sets the Main dispatcher to [testDispatcher]
 * for the duration of the test.
 */
class MainDispatcherRule(
  val testDispatcher: TestDispatcher = UnconfinedTestDispatcher()
) : TestWatcher() {
  override fun starting(description: Description) {
    super.starting(description)
    Dispatchers.setMain(testDispatcher)
  }
  override fun finished(description: Description) {
    super.finished(description)
    Dispatchers.resetMain()
  }
}

class MyViewModelTest {
  @get:Rule
  val mainDispatcherRule = MainDispatcherRule()
  ...
}

@HiltViewModel
class MyViewModel @Inject constructor(
  private val userRepository: UserRepository
) : ViewModel() {
  private val _userFlow = MutableStateFlow<UiState>(UiState.Loading)
  val userFlow: StateFlow<UiState> = _userFlow.asStateFlow()
  fun onRefresh() {
    viewModelScope.launch {
      userRepository
        .getUsers().asResult()
        .collect { result ->
          _userFlow.update {
            when (result) {
              is Result.Loading -> UiState.Loading
              is Result.Success -> UiState.Success(result.data)
              is Result.Error -> UiState.Error(result.exception)
            }
          }
        }
    }
  }
}

class MyViewModelTest{
    @get:Rule
    val mainDispatcherRule = MainDispatcherRule()
    // arrange
    private val repository = TestUserRepository()
    @OptIn(ExperimentalCoroutinesApi::class)
    @Test
    fun `when initialized, repository emits loading and data`() = runTest {
        // arrange
        val viewModel = MyViewModel(repository)
        val users = listOf(...)
        // 初始值應(yīng)該是UiState.Loading，因?yàn)閟tateFlow可以直接獲取最新值，此處直接做斷言
        assertEquals(UiState.Loading, viewModel.userFlow.value)
        // action
        repository.sendUsers(users)
        viewModel.onRefresh()
        //check
        assertEquals(UiState.Success(users), viewModel.userFlow.value)
    }
}
// Mock UserRepository
class TestUserRepository : UserRepository {
  /**
   * The backing hot flow for the list of users for testing.
   */
  private val usersFlow =
    MutableSharedFlow<List<User>>(replay = 1, onBufferOverflow = BufferOverflow.DROP_OLDEST)
  override fun getUsers(): Flow<List<User>> {
    return usersFlow
  }
  /**
   * A test-only API to allow controlling the list of users from tests.
   */
  suspend fun sendUsers(users: List<User>) {
    usersFlow.emit(users)
  }
}

@OptIn(ExperimentalCoroutinesApi::class)
@Test
fun `when initialized, repository emits loading and data`() = runTest {
    //arrange
    val viewModel = MainWithStateinViewModel(repository)
    val users = listOf(...)
    //action
    // 因?yàn)榇藭r(shí)collect操作并不是在ViewModel中，我們需要在測試代碼中執(zhí)行collect
    val collectJob = launch(UnconfinedTestDispatcher(testScheduler)) {
        viewModel.userFlow.collect()
    }
    //check
    assertEquals(UiState.Loading, viewModel.userFlow.value)
    //action
    repository.sendUsers(users)
    //check
    assertEquals(UiState.Success(users), viewModel.userFlow.value)
    collectJob.cancel()
}

@OptIn(ExperimentalCoroutinesApi::class)
@Test
fun `when initialized, repository emits loading and data`() = runTest {
    val viewModel = MainWithShareInViewModel(repository)
    val users = listOf(...)
    repository.sendUsers(users)
    viewModel.userFlow.test {
        val firstItem = awaitItem()
        assertEquals(UiState.Loading, firstItem)
        val secondItem = awaitItem()
        assertEquals(UiState.Success(users), secondItem)
    }
}