Why adding yeild() cause the unit test to fail?

How can I test a cooperative function for cancelation with the yeild() method?

I wrote a unit test for this repository and it passed but when I add yeild() method to make the refreshTitle method cooperative for cancellation then the unit test failed.

 suspend fun refreshTitle() {
    withContext(ioDispatcher) {
        try {
            val result = network.fetchNextTitle()
            //yield()    //by uncommenting this line the unit test fails.
            titleDao.insertTitle(Title(result))
        } catch (cause: Throwable) {
            throw TitleRefreshError("Unable to refresh title", cause)
        }
    }
}

This is the unit test:

 @Test
fun whenRefreshTitleSuccess_insertsRows() = runBlockingTest() {
    val titleDao = TitleDaoFake("title")
    val subject = TitleRepository(
        network = MainNetworkFake("OK"),
        titleDao = titleDao,
        ioDispatcher = TestCoroutineDispatcher(),
    )
    subject.refreshTitle()
    Truth.assertThat(titleDao.nextInsertedOrNull()).isEqualTo("OK")
}

The code comes from this android codelab: https://developer.android.com/codelabs/kotlin-coroutines#9

First I have to update these libraries to 1.7.1 version:

def coroutines_android_version = '1.7.1'
"org.jetbrains.kotlinx:kotlinx-coroutines-core:$coroutines_android_version",
"org.jetbrains.kotlinx:kotlinx-coroutines-android:$coroutines_android_version",
"org.jetbrains.kotlinx:kotlinx-coroutines-test:$coroutines_android_version"

To prevent this error I defined StandardTestDispatcher with the same TestCroutineScheduler as a field called standardTestDispatcher.

Detected use of different schedulers. If you need to use several test coroutine dispatchers, create one TestCoroutineScheduler and pass it to each of them.

and then changed the test function as follows:

private val scheduler = TestCoroutineScheduler()
private val standardTestDispatcher = StandardTestDispatcher(scheduler)

@Test
fun whenRefreshTitleSuccess_insertsRows() = runTest(
    context = standardTestDispatcher,
) {
    val titleDao = TitleDaoFake("title")
    val subject = TitleRepository(
        network = MainNetworkFake("OK"),
        titleDao = titleDao,
        ioDispatcher = standardTestDispatcher,
    )
    subject.refreshTitle()
    Truth.assertThat(titleDao.nextInsertedOrNull()).isEqualTo("OK")
}

Now I can test the cooperative function for cancellation successfully with yeild() method. It works without yeild().

suspend fun refreshTitle() {
    withContext(ioDispatcher) {
        try {
            val result = withTimeout(5_000) {
                network.fetchNextTitle()
            }
            yield()
            titleDao.insertTitle(Title(result))
        } catch (cause: Throwable) {
            throw TitleRefreshError("Unable to refresh title", cause)
        }
    }
}