刚开始测试我的compose视图模型，遇到了this文章。
snapshotFlow依赖于快照，当应用新快照时，而不仅仅是当值更改时，会发出新值。
下面是我测试这个视图模型的方法：

class SettingsViewModel @Inject constructor(
    userRepository: UserRepository
) : ViewModel() {
    private val _user = userRepository.getMe()
    private var _selectedAvatar by mutableStateOf<String?>(null)
    val state = combine(
        _user,
        snapshotFlow { _selectedAvatar },
    ) { user, selectedAvatar ->
        SettingsUiState(selectedAvatar ?: user?.avatar)
    }.stateIn(
        scope = viewModelScope,
        started = SharingStarted.WhileSubscribed(2_000),
        initialValue = SettingsUiState()
    )

    fun updateAvatar(imageUrl: String?) {
        _selectedAvatar = imageUrl
    }
}

data class SettingsUiState(
    val avatar: Any? = null
}

在实际测试中：

@OptIn(ExperimentalCoroutinesApi::class)
class SettingsViewModelTest {
    @get:Rule
    val mockkRule = MockKRule(this)

    @get:Rule
    val dispatcherRule = TestDispatcherRule()

    @MockK
    lateinit var userRepository: UserRepository

    lateinit var viewModel: SettingsViewModel

    @Test
    fun `state returns updated SettingsUiState when selectedAvatar updates`() = runTest {
        val selectedAvatar = "http://www.example.com/2.jpg"
        val user = User(1, "John", "http://www.example.com/1.jpg")

        every { userRepository.getMe() } returns flowOf(user)

        viewModel = SettingsViewModel(userRepository)

        viewModel.state.test {
            assertEquals(SettingsUiState(user.avatar), awaitItem())

            withMutableSnapshot { viewModel.updateAvatar(selectedAvatar) }
            assertEquals(SettingsUiState(selectedAvatar), awaitItem())
        }
    }
}

注意，我在.test内部调用updateAvatar(..)，涡轮机有一个关于如何测试共享流的参考。
另外，如果您的项目中还没有类似TestDispatcherRule的东西，这里有一个示例。