如何测试Kotlin挂起函数？单元测试遇类型转换异常

这个类型转换异常的核心原因是MockK链式调用的返回值层级错误：
你试图让apollo.buildApolloClient().query(...).execute().data直接返回GetDietaryRestrictionQuery.Data，但实际上execute()方法的返回值是ApolloResponse<GetDietaryRestrictionQuery.Data>，而非Data对象。你的Mock写法相当于强制让execute()返回了Data，导致实际代码调用execute().data时，会把Data对象当成ApolloResponse来处理，触发类型转换错误。

需要分层Mock Apollo调用链的每一步，确保每个方法返回对应类型的Mock对象，最后通过ApolloResponse包装你的Data对象返回。

修改后的测试代码如下：

@ExtendWith(MockKExtension::class)
internal class RecipeServiceImplTest {
    @MockK
    lateinit var apollo: ApolloClientConfig

    @MockK
    lateinit var mockApolloClient: ApolloClient

    @MockK
    lateinit var mockApolloCall: ApolloCall<GetDietaryRestrictionQuery.Data>

    @InjectMockKs
    lateinit var recipeService: RecipeServiceImpl

    @Test
    fun getDietaryRestrictionsTest() {
        val requestConfig = RequestConfig(
            Optional.presentIfNotNull("en"),
            Optional.presentIfNotNull(1)
        )
        val stringList: List<String> = listOf("ALCOHOL_FREE", "GLUTEN_FREE", "LACTOSE_FREE")
        val search: GetDietaryRestrictionQuery.Search = GetDietaryRestrictionQuery.Search(stringList)
        val data: GetDietaryRestrictionQuery.Data = GetDietaryRestrictionQuery.Data(search)

        // 1. Mock ApolloClientConfig返回mock的ApolloClient
        every { apollo.buildApolloClient() } returns mockApolloClient
        // 2. Mock ApolloClient的query方法返回mock的ApolloCall
        every { mockApolloClient.query(GetDietaryRestrictionQuery(requestConfig, 999)) } returns mockApolloCall
        // 3. Mock ApolloCall的execute()方法返回包装了Data的ApolloResponse
        coEvery { mockApolloCall.execute() } returns ApolloResponse.Builder(
            request = mockApolloCall.request(),
            data = data,
            responseCode = 200
        ).build()

        var result: GetDietaryRestrictionQuery.Data?
        runBlocking {
            result = recipeService.getDietaryRestrictions("en", 1)
        }

        // 分层验证调用次数
        verify(exactly = 1) { apollo.buildApolloClient() }
        verify(exactly = 1) { mockApolloClient.query(GetDietaryRestrictionQuery(requestConfig, 999)) }
        coVerify(exactly = 1) { mockApolloCall.execute() }
        
        assertEquals(data, result)
    }
}

• 新增mockApolloClient和mockApolloCall两个Mock对象，分别对应Apollo调用链的不同节点
• 拆分coEvery为三层，确保每个方法返回正确的类型：
  • buildApolloClient()返回ApolloClient
  • query(...)返回ApolloCall<Data>
  • execute()返回包装了目标Data的ApolloResponse
• 调整验证逻辑，分层验证每个节点的调用次数，避免链式验证的逻辑错误

内容的提问来源于stack exchange，提问作者engineering_the_future