Challenge 1: A Fake Repository and ViewModel Unit Test — Solution

class FakeTaskRepository : TaskRepository {
    private val _tasks = MutableStateFlow<List<Task>>(emptyList())
    override val tasks: Flow<List<Task>> = _tasks.asStateFlow()

    override suspend fun addTask(task: Task) {
        _tasks.value = _tasks.value + task
    }
}

@Test
fun `addTask adds the task to uiState`() = runTest {
    val fakeRepo = FakeTaskRepository()
    val viewModel = TaskViewModel(fakeRepo)

    viewModel.addTask("Buy milk")
    advanceUntilIdle()

    assertEquals(1, viewModel.uiState.value.tasks.size)
    assertEquals("Buy milk", viewModel.uiState.value.tasks.first().title)
}

Notes:
- FakeTaskRepository implements the TaskRepository INTERFACE (Course 2,
  Chapter 8) with a simple in-memory MutableStateFlow instead of Room —
  this is only possible because TaskViewModel's constructor demands the
  interface, not a concrete Room-backed implementation.
- runTest { } wraps the whole test body in a coroutine test scope;
  advanceUntilIdle() runs every pending coroutine (including
  viewModel.addTask's internal viewModelScope.launch, per Course 2
  Chapter 6) to completion before the assertions run, so the test
  doesn't race against still-pending async work.
- Because tasks is exposed via a StateFlow (built from a
  MutableStateFlow inside FakeTaskRepository), reading
  viewModel.uiState.value directly gives the CURRENT synchronous value —
  no separate collect{} needed just to check the test assertion.