Android 单元测试：如何模拟包含 MutableLiveData 但仅公开 LiveData 的对象？

Question

我有一个存储库类，它使用 MutableLiveData 对象（仅公开为 LiveData），将异步 Web 查询的结果返回到 ViewModel。然后，ViewModel 使用 Transformation 将结果映射到视图观察到的另一个 MutableLiveData。

我认为我通过分离关注点来遵循此模块中推荐的架构，但我发现很难为 ViewModel 编写单元测试：

class DataRepository ( private val webservice: DataWebService ) {

    private val _exception = MutableLiveData<Exception?>(null)
    val exception : LiveData<Exception?> get() = _exception

    private val _data = MutableLiveData<List<DataItem>>()

    val data: LiveData<List<DataItem>> = _data

    private val responseListener = Response.Listener<String> {response ->
        try {
            val list = JsonReader(SearchResult.mapping).readObject(response).map {
                    //Data transformation
            }
            _exception.value = null
            _data.value = list
        } catch (ex: Exception) {
            _exception.value = ex
            _data.value = emptyList()
        } 
    }

    fun findData(searchString: String) {
        _data.value = emptyList()
        webservice.findData(searchString, responseListener = responseListener)
    } 
}

class WebServiceDataViewModel (private val repository: DataRepository, app: App) : AndroidViewModel(app)
{

    val dataList: LiveData<List<DataItem>> = Transformations.map(repository.data) {
        _showEmpty.value = it.isEmpty()
        it
    }
    val exception: LiveData<Exception?> get() = repository.exception

    private val _showEmpty = MutableLiveData(true)
    val showEmpty : LiveData<Boolean> = _showEmpty

    private var _reloadOnCreate = true

    var searchString: String? = null
        set(value) {
            field = value
            if (!value.isNullOrBlank()) {
                repository.findData(value)
            }
        }
}

ViewModel 测试类：

@RunWith(JUnit4::class)
class WebServicePodcastViewModelTest {
    @Rule var instantExecutorRule = InstantTaskExecutorRule()

    @Mock lateinit var repository : DataRepository
    @Mock lateinit var app : App

    lateinit var viewModel: WebServiceDataViewModel

    @Mock lateinit var exceptionObserver : Observer<Exception?>
    @Mock lateinit var dataObserver : Observer<List<DataItem>>
    @Mock lateinit var showEmptyObserver : Observer<Boolean>

    @Before
    fun setUp() {
        MockitoAnnotations.initMocks(this)

        viewModel = WebServiceDataViewModel(repository, app)
        viewModel.exception.observeForever(exceptionObserver)
        viewModel.showEmpty.observeForever(showEmptyObserver)
        viewModel.dataList.observeForever(dataObserver)
    }

    @Test
    fun searchForData() {
        //given
        val searchString = "MockSearch"
        //when
        `when`(repository.findData(searchString)).then { /* How to invoke the mock repositories LiveData? */ }
        //then
        //TODO: verify that ViewModel LiveData behaves as expected
    }
}

那么如何调用模拟类的不可变 LiveData 呢？目前我正在尝试使用 Mockito 和 JUnit，但如果设置很简单，我愿意接受不同的框架！

Answer 1

最后我放弃了 Mockito 并使用了MockK，它的效果就像一个魅力！