安卓单元测试: How to mock an object which contains MutableLiveData but only exposes LiveData?

Question

我有一个存储库类，它使用一个 MutableLiveData 对象，仅作为 LiveData 公开，将异步 Web 查询的结果返回给 ViewModel。然后 ViewModel 使用 Transformation 将结果映射到 View 观察到的另一个 MutableLiveData。

我认为我通过分离关注点遵循了本模块中推荐的架构，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，但如果设置简单，我对不同的框架持开放态度!

Answer 1

最后我放弃了 Mockito 并使用了 MockK相反，它就像一个魅力!