cache.maxSize = 8
    taskFaker.runNextTask()
    set("a", "aa", "aa")
    set("b", "bb", "bbb")

    // Cause the cache trim job to fail.
    filesystem.setFaultyDelete(cacheDir / "a.0", true)
    taskFaker.runNextTask()

    // An edit should now add a job to clean up if the most recent trim failed.
    assertThat(cache.edit("b")).isNull()
    taskFaker.runNextTask()

 * deterministic.
 *
 * This class ensures that at most one thread is running at a time. This is initially the JUnit test
 * thread, which yields its execution privilege while calling [runTasks], [runNextTask], or
 * [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].