* [advanceUntil]. These functions don't return until the task threads are all idle.
 *
 * Task threads release their execution privilege in these ways:
 *
 *  * By yielding in [TaskRunner.Backend.coordinatorWait].
 *  * By yielding in [BlockingQueue.poll].
 *  * By completing.
 */
class TaskFaker : Closeable {
  @Suppress("NOTHING_TO_INLINE")
  internal inline fun Any.assertThreadHoldsLock() {