测试中 delay() 与 withTimeout() 协程的区别

Question

I'm writing some test case with coroutine

class ArticleViewModel : ViewModel() {
    private var likeCount = 0

    fun getLikeCount() = likeCount

    fun addLikeCount() {
        viewModelScope.launch {
            likeCount += 1
            likeCount
        }
    }
}

@ExperimentalCoroutinesApi
private fun MainCoroutineRule.runBlockingTest(block: suspend () -> Unit) =
    this.testDispatcher.runBlockingTest {
        block()
    }

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

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

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

@ExperimentalCoroutinesApi
class ArticleViewModelTest {
    @get:Rule
    var mainCoroutineRule = MainCoroutineRule()

    @Test
    fun addLikeCount() = mainCoroutineRule.runBlockingTest {
        val articleViewModel = ArticleViewModel()
        articleViewModel.addLikeCount()
        Assert.assertEquals(1, articleViewModel.getLikeCount())
    }
}

addLikeCount() test case above is working fine until I try to change logic addLikeCount().

case 1:

fun addLikeCount() {
        viewModelScope.launch {
            delay(2000)
            likeCount += 1
            likeCount
        }
    }

case 2:

fun addLikeCount() {
        viewModelScope.launch {
            withTimeout(2000) {
                likeCount += 1
                likeCount
            }
        }
    }

I want to delay 2 second (example: call API), then continuing handle logic (likeCount += 1, ....).

In case 1, addLikeCount() test case is fail

In case 2, addLikeCount() test case is pass

I don't know why? what is difference between delay vs withTimeout? If you understand my problem, please help me. Thank you so much.

Answer 1

withTimeout立即推进时间，但在启动时，您需要使用advanceUntilIdle或advanceUntilIdle advanceTimeBy(2000)将时间移动到您可以在事件状态之前、中间或之后的位置。