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 class，它使用 MutableLiveData 对象（仅作为 LiveData 公开）到 return 对 ViewModel 的异步 Web 查询结果。 ViewModel 然后使用 Transformation 将结果映射到另一个 MutableLiveData，该数据由 View 观察。

我想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class:

@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 class 的不可变 LiveData？目前我正在尝试使用 Mockito 和 JUnit，但如果设置简单，我愿意接受不同的框架！

Answer 1

最后我放弃了 Mockito，改用了 MockK，效果非常好！

Answer 2

你必须考虑到你需要在测试中设置和观察从视图观察到的实时数据，那么你可以这样做：（作为一种好的做法，您可以使用带有泛型的 Sealed Class 来封装您的 UI 的状态并促进观察不同实时数据的过程，而不是根据类型 od 结果使用不同的 Livedata不仅仅是一个）

@RunWith(MockitoJUnitRunner::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() {
    viewModel = WebServiceDataViewModel(repository, app)
    viewModel.exception.observeForever(exceptionObserver)
    viewModel.showEmpty.observeForever(showEmptyObserver)
    viewModel.dataList.observeForever(dataObserver)
  }

  @Test
  fun searchForData() {
    //given
    val searchString = "MockSearch"
    val dataResponse = MutableLiveData<List<DataItem>>()
    dataResponse.value = listOf<DataItem>()
    //when
    `when`(repository.findData(searchString)).then { 
         dataResponse
    }
    //then
    assertNotNull(viewModel.getDataList().value)
    assertEquals(viewModel.getDataList().value,  emptyList()) /* empty list must be an object of the same type of listOf<DataItem>() */
 }
}

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

Android Unit Test: How to mock an object which contains MutableLiveData but only exposes LiveData?

junit

android

mockito

android-livedata

mutablelivedata