接收流的Android单元测试视图模型

Question

我有一个 ViewModel 与用例对话并返回一个流，即Flow<MyResult>. 我想对我的 ViewModel 进行单元测试。我是使用流程的新手。需要帮助请。这是下面的视图模型 -

class MyViewModel(private val handle: SavedStateHandle, private val useCase: MyUseCase) : ViewModel() {

        private val viewState = MyViewState()

        fun onOptionsSelected() =
            useCase.getListOfChocolates(MyAction.GetChocolateList).map {
                when (it) {
                    is MyResult.Loading -> viewState.copy(loading = true)
                    is MyResult.ChocolateList -> viewState.copy(loading = false, data = it.choclateList)
                    is MyResult.Error -> viewState.copy(loading = false, error = "Error")
                }
            }.asLiveData(Dispatchers.Default + viewModelScope.coroutineContext)

MyViewState 看起来像这样 -

 data class MyViewState(
        val loading: Boolean = false,
        val data: List<ChocolateModel> = emptyList(),
        val error: String? = null
    )

单元测试如下所示。断言失败总是不知道我在那里做错了什么。

class MyViewModelTest {

    @get:Rule
    val instantExecutorRule = InstantTaskExecutorRule()

    private val mainThreadSurrogate = newSingleThreadContext("UI thread")

    private lateinit var myViewModel: MyViewModel

    @Mock
    private lateinit var useCase: MyUseCase

    @Mock
    private lateinit var handle: SavedStateHandle

    @Mock
    private lateinit var chocolateList: List<ChocolateModel>

    private lateinit var viewState: MyViewState


    @Before
    fun setup() {
        MockitoAnnotations.initMocks(this)
        Dispatchers.setMain(mainThreadSurrogate)
        viewState = MyViewState()
        myViewModel = MyViewModel(handle, useCase)
    }

    @After
    fun tearDown() {
        Dispatchers.resetMain() // reset main dispatcher to the original Main dispatcher
        mainThreadSurrogate.close()
    }

    @Test
    fun onOptionsSelected() {
        runBlocking {
            val flow = flow {
                emit(MyResult.Loading)
                emit(MyResult.ChocolateList(chocolateList))
            }

            Mockito.`when`(useCase.getListOfChocolates(MyAction.GetChocolateList)).thenReturn(flow)
            myViewModel.onOptionsSelected().observeForever {}

            viewState.copy(loading = true)
            assertEquals(viewState.loading, true)

            viewState.copy(loading = false, data = chocolateList)
            assertEquals(viewState.data.isEmpty(), false)
            assertEquals(viewState.loading, true)
        }
    }
}

Answer 1

此测试环境中存在的问题很少：

1. 该flow生成器将立即发出这样的结果总是最后一个值将被接收。
2. viewState持有者与我们的模拟没有联系，因此是无用的。
3. 要测试具有多个值的实际流量，需要延迟和快进控制。
4. 需要收集响应值以进行断言

解决方案：

1. 使用delay在流生成器来处理这两个值
2. 删除viewState。
3. 使用MainCoroutineScopeRule控制与延迟执行流程
4. 要为断言收集观察者值，请使用ArgumentCaptor。

源代码：

1. MyViewModelTest.kt

   import androidx.arch.core.executor.testing.InstantTaskExecutorRule
   import androidx.lifecycle.Observer
   import androidx.lifecycle.SavedStateHandle
   import com.pavneet_singh.temp.ui.main.testflow.*
   import org.junit.Assert.assertEquals
   import kotlinx.coroutines.delay
   import kotlinx.coroutines.flow.flow
   import kotlinx.coroutines.runBlocking
   import org.junit.Before
   import org.junit.Rule
   import org.junit.Test
   import org.mockito.ArgumentCaptor
   import org.mockito.Captor
   import org.mockito.Mock
   import org.mockito.Mockito.*
   import org.mockito.MockitoAnnotations
   
   class MyViewModelTest {
   
       @get:Rule
       val instantExecutorRule = InstantTaskExecutorRule()
   
       @get:Rule
       val coroutineScope = MainCoroutineScopeRule()
   
       @Mock
       private lateinit var mockObserver: Observer<MyViewState>
   
       private lateinit var myViewModel: MyViewModel
   
       @Mock
       private lateinit var useCase: MyUseCase
   
       @Mock
       private lateinit var handle: SavedStateHandle
   
       @Mock
       private lateinit var chocolateList: List<ChocolateModel>
   
       private lateinit var viewState: MyViewState
   
       @Captor
       private lateinit var captor: ArgumentCaptor<MyViewState>
   
   
       @Before
       fun setup() {
           MockitoAnnotations.initMocks(this)
           viewState = MyViewState()
           myViewModel = MyViewModel(handle, useCase)
       }
   
       @Test
       fun onOptionsSelected() {
           runBlocking {
               val flow = flow {
                   emit(MyResult.Loading)
                   delay(10)
                   emit(MyResult.ChocolateList(chocolateList))
               }
   
               `when`(useCase.getListOfChocolates(MyAction.GetChocolateList)).thenReturn(flow)
               `when`(chocolateList.get(0)).thenReturn(ChocolateModel("Pavneet", 1))
               val liveData = myViewModel.onOptionsSelected()
               liveData.observeForever(mockObserver)
   
               verify(mockObserver).onChanged(captor.capture())
               assertEquals(true, captor.value.loading)
               coroutineScope.advanceTimeBy(10)
               verify(mockObserver, times(2)).onChanged(captor.capture())
               assertEquals("Pavneet", captor.value.data[0].name)// name is custom implementaiton field of `ChocolateModel` class
           }
       }
   }
   

2. MainCoroutineScopeRule.kt源文件复制

3. 清单 dependencies

   dependencies {
       implementation fileTree(dir: 'libs', include: ['*.jar'])
       implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
       implementation 'androidx.appcompat:appcompat:1.1.0'
       implementation 'androidx.core:core-ktx:1.2.0'
       implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
       implementation 'androidx.lifecycle:lifecycle-extensions:2.2.0'
       implementation 'androidx.lifecycle:lifecycle-viewmodel-ktx:2.2.0'
       testImplementation 'junit:junit:4.12'
       androidTestImplementation 'androidx.test.ext:junit:1.1.1'
       androidTestImplementation 'androidx.test.espresso:espresso-core:3.2.0'
       implementation 'androidx.lifecycle:lifecycle-livedata-ktx:2.3.0-alpha01'
       implementation 'org.mockito:mockito-core:2.16.0'
       testImplementation 'androidx.arch.core:core-testing:2.1.0'
       testImplementation 'org.jetbrains.kotlinx:kotlinx-coroutines-test:1.3.5'
       testImplementation 'org.mockito:mockito-inline:2.13.0'
   }
   

输出（通过删除一些延迟的帧来优化 gif）：

在 Github 上查看mvvm-flow-coroutine-testing repo 以获得完整的实现。