Kotlin Android测试报错Live Data Value未设置，已尝试多种方法仍无效

我是Kotlin Android新手，在学习测试时遇到错误，提示“Live Data Value was never set”，即便使用了advanceUntilIdle也无法解决。实际运行正常，但测试时出现该问题。

相关代码 #

Repository代码 #

class UserRepository private constructor(
    private val userPreference: UserPreference,
    private val apiService: ApiService
) {
  
    private val _loginResponse = MutableLiveData<LoginResponse?>()
    val loginResponse: LiveData<LoginResponse?> = _loginResponse

    private val _errorLoginMessage = MutableLiveData<String?>()
    val errorLoginMessage: LiveData<String?> = _errorLoginMessage

    fun login(email: String, password: String) {
        _showLoading.value = true
        val client = apiService.login(email, password)

        client.enqueue(object : Callback<LoginResponse> {
            override fun onResponse(
                call: Call<LoginResponse>, response: Response<LoginResponse>
            ) {
                _showLoading.value = false
                Log.d(TAG, "Register Response : ${response.body()}")
                if (response.isSuccessful && response.body() != null) {
                    _loginResponse.value = response.body()
                } else {
                    _errorLoginMessage.value = response.message()
                    Log.e(TAG, "onFailure: ${response.message()}")
                }
            }

            override fun onFailure(call: Call<LoginResponse>, t: Throwable) {
                _showLoading.value = false
                _errorLoginMessage.value = t.message
                Log.e(TAG, "onFailure: ${t.message}")
            }
        })
    }
}

ViewModel代码 #

class LoginViewModel(private val repository: UserRepository) : ViewModel() {

    val loginResponse: LiveData<LoginResponse?> = repository.loginResponse
    val errorMessage = repository.errorLoginMessage

    fun login(email: String, password: String) {
        repository.login(email, password)
    }
}

测试代码 #

@RunWith(RobolectricTestRunner::class)
class LoginViewModelTest {

    private lateinit var viewModel: LoginViewModel
    private val context = RuntimeEnvironment.getApplication().applicationContext

    @get:Rule
    val instantTaskExecutorRule = InstantTaskExecutorRule()

    @Before
    fun setup() {
        val userRepository = UserRepository.getInstance(
            UserPreference.getInstance(context.dataStore)
        )

        viewModel = LoginViewModel(
            userRepository
        )

        Dispatchers.setMain(StandardTestDispatcher())
    }

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

    @Test
    fun `Test Login Failed`() = runTest {
        viewModel.login("testWrongEmail@gmail.com", "testWrongPassword")
        advanceUntilIdle()
        val result = viewModel.loginResponse.getOrAwaitValue()
        Assert.assertEquals(true, result?.error)
        Assert.assertEquals("failed", result?.message)
    }
}

我已尝试添加InstantTaskExecutorRule、设置主调度器、使用runTest，还将enqueue改为execute，但问题仍未解决，请问这是为什么？

你的问题出在两个核心点：

1. 测试用了真实网络请求：OkHttp的异步回调不在协程调度体系内，advanceUntilIdle管不到，测试环境也不会自动触发真实网络请求的回调，导致LiveData没被赋值。
2. 测试逻辑匹配错误：登录失败场景下，原代码只会更新errorLoginMessage，不会更新loginResponse，你硬要拿loginResponse的值来断言，自然会触发“值未设置”的错误。

具体解决步骤 #

1. 改造Repository的依赖注入

让UserRepository的getInstance支持传入自定义的ApiService，方便测试时替换成模拟对象：

class UserRepository private constructor(
    private val userPreference: UserPreference,
    private val apiService: ApiService
) {
    companion object {
        @Volatile
        private var INSTANCE: UserRepository? = null

        // 新增apiService参数，默认用真实实例，测试时传模拟实例
        fun getInstance(
            userPreference: UserPreference,
            apiService: ApiService = RetrofitClient.instance.create(ApiService::class.java)
        ): UserRepository {
            return INSTANCE ?: synchronized(this) {
                INSTANCE ?: UserRepository(userPreference, apiService).also { INSTANCE = it }
            }
        }
    }

    // 原有代码不变...
}

2. 用Mockito模拟ApiService

测试时不要用真实网络，直接模拟ApiService的返回结果：

@RunWith(RobolectricTestRunner::class)
class LoginViewModelTest {

    private lateinit var viewModel: LoginViewModel
    // 模拟ApiService
    private val mockApiService: ApiService = mock(ApiService::class.java)
    private val context = RuntimeEnvironment.getApplication().applicationContext

    @get:Rule
    val instantTaskExecutorRule = InstantTaskExecutorRule()

    @Before
    fun setup() {
        val userRepository = UserRepository.getInstance(
            UserPreference.getInstance(context.dataStore),
            mockApiService // 传入模拟的ApiService
        )

        viewModel = LoginViewModel(userRepository)
        Dispatchers.setMain(StandardTestDispatcher())
    }

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

    @Test
    fun `Test Login Failed`() = runTest {
        // 模拟登录失败的响应
        val errorResponseBody = ResponseBody.create(
            MediaType.parse("application/json"),
            "{\"error\":true,\"message\":\"failed\"}"
        )
        val mockErrorResponse = Response.error<LoginResponse>(401, errorResponseBody)
        
        // 指定当调用login方法时返回模拟的失败响应
        `when`(mockApiService.login(anyString(), anyString())).thenReturn(object : Call<LoginResponse> {
            override fun execute(): Response<LoginResponse> = mockErrorResponse
            override fun enqueue(callback: Callback<LoginResponse>) {
                callback.onResponse(this, mockErrorResponse)
            }
            override fun isExecuted(): Boolean = false
            override fun cancel() {}
            override fun isCanceled(): Boolean = false
            override fun request(): Request = Request.Builder().url("http://test.com").build()
            override fun clone(): Call<LoginResponse> = this
        })

        viewModel.login("testWrongEmail@gmail.com", "testWrongPassword")
        advanceUntilIdle()

        // 登录失败时应该断言errorMessage，而非loginResponse
        val errorMsg = viewModel.errorMessage.getOrAwaitValue()
        // 若要匹配"failed"，可修改模拟逻辑让response.message()返回该值，或直接模拟回调设置_errorLoginMessage
        Assert.assertEquals("failed", errorMsg)
    }
}

3. 修正测试断言逻辑

登录失败时，原代码会走onResponse的else分支，设置_errorLoginMessage为response.message()，所以测试时应该监听errorMessage，而不是loginResponse——后者在失败场景下根本不会被赋值，这是你之前测试报错的直接原因。

额外提醒 #

• 测试异步逻辑时，永远用模拟对象替代真实依赖，真实网络、数据库等操作在测试中不稳定且耗时。
• advanceUntilIdle只能等待协程调度器中的任务，OkHttp、RxJava等其他异步框架的任务需要单独处理，或者用模拟对象同步返回结果。

内容的提问来源于stack exchange，提问作者Diki Dimal