ViewModel 单元测试（JUnit5、CoroutineDispatcher、Turbine、Mockk）未按预期工作

Question

我正在尝试了解 Turbine 如何与

StateFlow

一起工作。

HelloWorldView模型

import androidx.lifecycle.ViewModel
import androidx.lifecycle.viewModelScope
import kotlinx.coroutines.CoroutineDispatcher
import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.delay
import kotlinx.coroutines.flow.MutableStateFlow
import kotlinx.coroutines.flow.StateFlow
import kotlinx.coroutines.flow.asStateFlow
import kotlinx.coroutines.launch

class HelloWorldViewModel(
    private val dispatcher: CoroutineDispatcher = Dispatchers.IO,
    private val doOperationUseCase: DoOperationUseCase
) : ViewModel() {

    private val _state: MutableStateFlow<HelloWorldState> = MutableStateFlow(HelloWorldState())
    val state: StateFlow<HelloWorldState> = _state.asStateFlow()

    fun doOperation() {
        viewModelScope.launch(dispatcher) {
            _state.emit(state.value.copy(loading = true))
            doOperationUseCase()
            _state.emit(state.value.copy(loading = false))
        }
    }

}

你好世界状态

data class HelloWorldState(val loading: Boolean = false)

DoOperationUseCase

class DoOperationUseCase {
    suspend operator fun invoke(): Result<List<String>> {
        delay(500)
        return Result.success(listOf("1"))
    }
}

HelloWorldViewModel测试

import app.cash.turbine.test
import io.mockk.coEvery
import io.mockk.impl.annotations.MockK
import io.mockk.junit5.MockKExtension
import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.ExperimentalCoroutinesApi
import kotlinx.coroutines.test.TestDispatcher
import kotlinx.coroutines.test.UnconfinedTestDispatcher
import kotlinx.coroutines.test.resetMain
import kotlinx.coroutines.test.runTest
import kotlinx.coroutines.test.setMain
import org.junit.jupiter.api.AfterEach
import org.junit.jupiter.api.Assertions.*
import org.junit.jupiter.api.BeforeEach
import org.junit.jupiter.api.Test
import org.junit.jupiter.api.extension.ExtendWith

@OptIn(ExperimentalCoroutinesApi::class)
@ExtendWith(MockKExtension::class)
class HelloWorldViewModelTest {

    private val testDispatcher: TestDispatcher = UnconfinedTestDispatcher()

    @MockK
    lateinit var doOperationUseCase: DoOperationUseCase

    private lateinit var classUnderTest: HelloWorldViewModel

    @BeforeEach
    fun setUp() {
        Dispatchers.setMain(testDispatcher)
        classUnderTest = HelloWorldViewModel(testDispatcher, doOperationUseCase)
    }

    @AfterEach
    fun tearDown() {
        Dispatchers.resetMain()
    }

    @Test
    fun doOperation() = runTest {

        coEvery { doOperationUseCase() } returns Result.success(listOf(""))
        assertEquals(HelloWorldState(), classUnderTest.state.value) // expected for initial state
        classUnderTest.state.test {
            classUnderTest.doOperation()
            assertEquals(classUnderTest.state.value.copy(loading = true), awaitItem()) // expected before calling doOperationUseCase use case
            assertEquals(classUnderTest.state.value.copy(loading = false), awaitItem()) // expected after calling doOperationUseCase use case
        }
    }
}

结果：

No value produced in 3s
app.cash.turbine.TurbineAssertionError: No value produced in 3s

仅在以下情况下测试成功：

@Test
fun doOperation() = runTest {

    coEvery { doOperationUseCase() } returns Result.success(listOf(""))

    classUnderTest.state.test {
        classUnderTest.doOperation()
        assertEquals(classUnderTest.state.value.copy(loading = false), awaitItem())
    }
}

依赖关系：

testRuntimeOnly("org.junit.jupiter:junit-jupiter-engine:5.8.2")
testImplementation("org.junit.platform:junit-platform-console:1.8.2")
testImplementation("org.junit.jupiter:junit-jupiter-api:5.8.2")
testImplementation("org.junit.jupiter:junit-jupiter-params:5.8.2")
testImplementation("app.cash.turbine:turbine:1.0.0")
testImplementation("io.mockk:mockk:1.13.8")
testImplementation("com.google.truth:truth:1.1.4")

Google 文档没有帮助，因为存储库控制何时发出新值。

Answer 1

您可以创建自定义范围来帮助编写测试用例，而不是使用默认的

viewModelScope

扩展属性。

这是上面代码中问题的解决方案。

步骤1

为 ViewModel 创建自定义可关闭范围

import java.io.Closeable
import kotlinx.coroutines.CoroutineScope
import kotlin.coroutines.CoroutineContext

class CloseableCoroutineScope(context: CoroutineContext) : Closeable,    CoroutineScope {
  override val coroutineContext: CoroutineContext = context
  override fun close() {
    coroutineContext.cancel()
  }
}

注意：我是直接从aac ViewModel.kt ext（package androidx.lifecycle）

复制的

第2步

在 ViewModel 中使用此自定义范围

class HelloWorldViewModel(
  private val customScope: CloseableCoroutineScope = CloseableCoroutineScope(SupervisorJob() + Dispatchers.Main.immediate),
  private val dispatcher: CoroutineDispatcher = Dispatchers.IO,
  private val doOperationUseCase: DoOperationUseCase
): ViewModel(customScope) {
  private val _state: MutableStateFlow<HelloWorldState> = MutableStateFlow(HelloWorldState())
  val state: StateFlow<HelloWorldState> = _state.asStateFlow()

  fun doOperation() {
    customScope.launch(dispatcher) {
      _state.emit(state.value.copy(loading = true))
      doOperationUseCase()
      _state.emit(state.value.copy(loading = false))
    }
  }
}

第3步

然后更新您的测试以使用测试范围和调度程序

@OptIn(ExperimentalCoroutinesApi::class)
@ExtendWith(MockKExtension::class)
class HelloWorldViewModelTest {
  private val testDispatcher: TestDispatcher = UnconfinedTestDispatcher()
  var doOperationUseCase = DoOperationUseCase()
  private lateinit var classUnderTest: HelloWorldViewModel

  @Test
  fun doOperation() = runTest(testDispatcher) {
    classUnderTest = HelloWorldViewModel(CloseableCoroutineScope(this.coroutineContext), testDispatcher, doOperationUseCase)
    assertEquals(HelloWorldState(), classUnderTest.state.value) // expected for initial state
    classUnderTest.doOperation()
    classUnderTest.state.test {
      assertEquals(classUnderTest.state.value.copy(loading = true), awaitItem()) // expected before calling doOperationUseCase use case
      assertEquals(classUnderTest.state.value.copy(loading = false), awaitItem()) // expected after calling doOperationUseCase use case
    }
  }
}

我已经测试了这个解决方案并且它有效。 附加提示：

• 我还建议使用 test doubles 而不是模拟。这意味着，您可以为 DoOperationUseCase 创建一个接口并创建一个假实现。
• 您可以使用动态注入来创建范围并注入到 ViewModel
• 欲了解更多信息，您可以查看这篇文章。