Android单元测试:如何模拟一个包含MutableLiveData但只公开LiveData的对象

Question

我有一个存储库类，它使用MutableLiveData对象(仅作为LiveData公开(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View观察到的另一个MutableLiveData。

我想我遵循了本模块中推荐的体系结构，将关注点分开，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，我该如何调用一个模拟类的不可变LiveData呢？目前我正在尝试使用Mockito&JUnit，但如果设置简单，我对不同的框架持开放态度！

Answer 1

您必须考虑到您需要在测试中设置和观察从视图中观察到的livedata，然后您可以执行以下操作：(作为一种良好的实践，您可以使用带有泛型的Sealed Class来封装UI的状态，并促进观察不同实时数据的过程，而不仅仅是一个(

@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>() */
}
}

Answer 2

最后我抛弃了Mockito，改为使用MockK，这就像一个符咒！