使用Mockito模拟挂起函数返回null

Question

我有以下几门课

interface CarsApi {
    suspend fun fetchCar() : Car
}

class FetchCarUseCase(private val carsApi: CarsApi) {
    suspend fun execute: Car = withContext(dispatcherProvider.io()) {
        carsApi.fetchCar()
    }
}

class ViewModel(private val fetchCarUseCase: FetchCarUseCase) {

     private var car: Car

     suspend fun retrieveCar() {
        car = fetchCarUseCase.execute()
     }
}

我想为viewModel和UseCase编写一个ermetic测试：

@Test
fun testCarFetching() = runBlockingTest {
  val aCar = Car()
  val mockApi = mock<CarsApi>()
  `when`(mockApi.fetchCar()).thenReturn(aCar)
  val fetchCarUseCase = FetchCarUseCase(mockApi)
  val viewModel = ViewModel(fetchCarUseCase)

  viewModel.retrieveCar()

  /* assert stuff on viewModel.car*/
}

但ViewModel.car似乎总是为空。在测试体中mockapi.fetchcar（）检索提供的值，但在FetchCarUseCase中不检索。此外，如果我从界面中移除suspend关键字，那么嘲弄似乎可以很好地工作。

目前，由于一些其他条件，我无法使用Mockk库，所以我只能使用mockito。

我是不是漏掉了什么？

使用的依赖项：testImplementation“junit：junit：4.12”testImplementation“org.mockito:mockito-core：2.28.2”testImplementation（“com.nhaarman.mockitokotlin2:mockito-kotlin:2.1.0"）{exclude module：”mockito-core“}testImplementation”org.jetbrains.kotlinx:kotlinx-coroutines-test:1.3.2

Answer 1

万一其他人必须处理这个问题，这里是我已经建立的基础设施。

首先，在启动线程的所有类中，通过构造函数或属性注入一个kotlinx.coroutines.DispatcherProvider。在我的例子中，它只是useCase，但viewModel也可能需要它。

    class FetchCarUseCase(private val dispatcher: CoroutineDispatcher,
                          private val carsApi: CarsApi) {
    suspend fun execute: Car = withContext(dispatcher) {
        carsApi.fetchCar()
    }
}

在单元测试项目中，添加一个帮助器规则类，以提取某些功能：

 @ExperimentalCoroutinesApi
class CoroutineTestRule(val testDispatcher: TestCoroutineDispatcher = TestCoroutineDispatcher()) : TestWatcher() {

    val testDispatcherProvider = object : DispatcherProvider {
        override fun default(): CoroutineDispatcher = testDispatcher
        override fun io(): CoroutineDispatcher = testDispatcher
        override fun main(): CoroutineDispatcher = testDispatcher
        override fun unconfined(): CoroutineDispatcher = testDispatcher
    }

    override fun starting(description: Description?) {
        super.starting(description)
        Dispatchers.setMain(testDispatcher)
    }

    override fun finished(description: Description?) {
        super.finished(description)
        Dispatchers.resetMain()
        testDispatcher.cleanupTestCoroutines()
    }
}

最后单元测试如下所示：

    @ExperimentalCoroutinesApi
    @RunWith(MockitoJUnitRunner::class)
    class ViewModelTest {
        @get:Rule
        var coroutinesTestRule = CoroutineTestRule()

        @Test
    fun testCarFetching() = coroutinesTestRule.testDispatcher.runBlockingTest {
      val aCar = Car()
      val mockApi = mock<CarsApi>()
      `when`(mockApi.fetchCar()).thenReturn(aCar)
      val fetchCarUseCase = FetchCarUseCase(mockApi)
      val viewModel = ViewModel(fetchCarUseCase)

      viewModel.retrieveCar()

      /* assert stuff on viewModel.car*/
    }

   @Test
    fun testCarFetchingError() = coroutinesTestRule.testDispatcher.runBlockingTest {
      val aCar = Car()
      val mockApi = mock<CarsApi>()
      `when`(mockApi.fetchCar()).then {
            throw Exception()
        }

      val fetchCarUseCase = FetchCarUseCase(mockApi)
      val viewModel = ViewModel(fetchCarUseCase)

      viewModel.retrieveCar()

      /* assert stuff on erros*/
    }
}

这样，单元测试中的所有代码都运行在同一线程和同一上下文中。