* is to avoid unnecessary stalls in situations like this: A RateLimiter of 1qps, and 4 threads,
     * all calling acquire() at these moments:
     *
     * T0 at 0 seconds
     * T1 at 1.05 seconds
     * T2 at 2 seconds
     * T3 at 3 seconds
     *
     * Due to the slight delay of T1, T2 would have to sleep till 2.05 seconds, and T3 would also
     * have to sleep till 3.05 seconds.
     */

      assertFalse(keys.remove(null));
      assertFalse(keys.remove(6));
      assertFalse(keys.remove(-6));
      assertFalse(keys.removeAll(asList(null, 0, 15, 1500)));
      assertFalse(keys.retainAll(asList(null, 0, 15, 1500)));
      checkEmpty(keys);
      checkEmpty(cache);
    }
  }

  public void testKeySet_remove() {
    for (LoadingCache<Object, Object> cache : caches()) {

    TimedWaiterThread thread =
        new TimedWaiterThread(new AbstractFuture<Object>() {}, 2, TimeUnit.SECONDS);
    thread.start();
    thread.awaitWaiting();
    thread.suspend();
    // Sleep for enough time to add 1500 milliseconds of overwait to the get() call.
    long toWaitMillis = 3500 - TimeUnit.NANOSECONDS.toMillis(System.nanoTime() - thread.startTime);
    Thread.sleep(toWaitMillis);
    thread.setPriority(Thread.MAX_PRIORITY);

      assertFalse(keys.remove(null));
      assertFalse(keys.remove(6));
      assertFalse(keys.remove(-6));
      assertFalse(keys.removeAll(asList(null, 0, 15, 1500)));
      assertFalse(keys.retainAll(asList(null, 0, 15, 1500)));
      checkEmpty(keys);
      checkEmpty(cache);
    }
  }

  public void testKeySet_remove() {
    for (LoadingCache<Object, Object> cache : caches()) {

    Stopwatch stopwatch = Stopwatch.createStarted();
    Condition condition = TestCondition.createAndSignalAfter(500, MILLISECONDS);

    boolean signaledBeforeTimeout = awaitUninterruptibly(condition, 1500, MILLISECONDS);

    assertTrue(signaledBeforeTimeout);
    assertTimeNotPassed(stopwatch, LONG_DELAY_MS);
    assertNotInterrupted();
  }

  public void testConditionAwaitInterruptedTimeoutExceeded() {

    Stopwatch stopwatch = Stopwatch.createStarted();
    Condition condition = TestCondition.createAndSignalAfter(500, MILLISECONDS);

    boolean signaledBeforeTimeout = awaitUninterruptibly(condition, 1500, MILLISECONDS);

    assertTrue(signaledBeforeTimeout);
    assertTimeNotPassed(stopwatch, LONG_DELAY_MS);
    assertNotInterrupted();
  }

  public void testConditionAwaitInterruptedTimeoutExceeded() {

    TimedWaiterThread thread =
        new TimedWaiterThread(new AbstractFuture<Object>() {}, 2, TimeUnit.SECONDS);
    thread.start();
    thread.awaitWaiting();
    thread.suspend();
    // Sleep for enough time to add 1500 milliseconds of overwait to the get() call.
    long toWaitMillis = 3500 - TimeUnit.NANOSECONDS.toMillis(System.nanoTime() - thread.startTime);
    Thread.sleep(toWaitMillis);
    thread.setPriority(Thread.MAX_PRIORITY);

    X489,
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