Difference between delay() vs withTimeout() coroutine in Testing

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.

The difference is `delay` suspends the Execution on other hand `withTimeout` just add a timeout to the execution once timeout is reached before execution completes it with throw a `CancelationException` . U should have a look at [This](https://stackoverflow.com/questions/47171302/unit-testing-a-kotlin-coroutine-with-delay) and [This](https://stackoverflow.com/questions/57496946/why-unit-tests-with-coroutines-delay-fails). — ADM, Sep 07 '20 at 05:24

score 0 · Answer 1 · answered Sep 07 '20 at 05:22

0

withTimeout advances time instantly but with launch you need to use advanceUntilIdle or advanceTimeBy(2000) to move time where you can prior, middle or after states of events.

answered Sep 07 '20 at 05:22

Thracian

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Difference between delay() vs withTimeout() coroutine in Testing

1 Answers1