UnconfinedTestDispatcher documentation is unclear about delay and virtual time

[GabrielBrasileiro]

Context:

The current documentation is unclear about how delay behaves when using UnconfinedTestDispatcher.

The phrase “it skips delays” can reasonably be interpreted as delayed coroutines resuming immediately when delay() is called inside the coroutine block.

The actual execution semantics are not clearly described, and this part of the documentation could be improved.

Page:

https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-test/kotlinx.coroutines.test/-unconfined-test-dispatcher.html

Section:

This dispatcher is similar to Dispatchers.Unconfined: the tasks that it executes are not confined to any particular thread and form an event loop; it's different in that it skips delays, as all TestDispatchers do.

Test:

@Test
fun unconfinedTestDispatcherDelay() = runTest {
    val dispatcher = UnconfinedTestDispatcher(testScheduler)

    var resumed = false

    launch(dispatcher) {
        delay(100)
        resumed = true
    }

    // At this point, resumed is false
    assertFalse(resumed)

    testScheduler.advanceUntilIdle()

    assertTrue(resumed)
}

[dkhalanskyjb]

Hi! At the bottom of the document, there's a paragraph starting with

In order to support delay skipping [...]

Linking it to https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-test/kotlinx.coroutines.test/-test-coroutine-scheduler/, which is the mechanism for delay-skipping. Does this answer your question?