i'm writing a custom `test` operator for testing `...

# coroutines

[tseisel]

i'm writing a custom test operator for testing Flow. Here is the current API :

val flow = flow {
    emit(0)
    emit(1)
    emit(2)
    delay(200)
    emit(3)
    delay(500)
    throw Exception("Flow failure")
}

// At this point, subscribe to the source flow. 
// Elements are collected manually to test various scenarios such as backpressure or triggering listeners.
flow.test { /* this = TestCollector<Int> */
    // Expect to receive exactly 1 element right now. It is collected to the "values" list.
    // This fails if the flow terminates, throws an exception or the element is not available right now.
    expect(1)
    assertEquals(0, values[0])

    // You can collect multiple elements at once.
    expect(2)
    assertEquals(1, values[1])
    assertEquals(2, values[2])

    // When expecting to collect elements within a time delay, use the variant with duration parameter.
    // I may replace TimeUnit with the new Duration class from kotlin.time when more stable.
    expect(1, 200, TimeUnit.MILLISECONDS)
    assertEquals(3, values[3])

    // You can also expect exceptions.
    val failure = expectFailure()
    assertEquals("Flow failure", failure.message)
}

My questions are :
1. Do some of you need this kind of API ? If yes, does the current API satisfy your needs ? What feature would you add ?
2. Is something similar already planned for kotlinx.coroutines.test, or is there any library that already provide this feature ?