Monitor monitor1 = new Monitor();
    Monitor monitor2 = new Monitor();
    FlagGuard guard = new FlagGuard(monitor2);
    assertThrows(IllegalMonitorStateException.class, () -> monitor1.getWaitQueueLength(guard));
  }

  public void testHasWaitersWithWrongMonitorThrowsIMSE() {
    Monitor monitor1 = new Monitor();
    Monitor monitor2 = new Monitor();
    FlagGuard guard = new FlagGuard(monitor2);

    Monitor monitor1 = new Monitor();
    Monitor monitor2 = new Monitor();
    FlagGuard guard = new FlagGuard(monitor2);
    assertThrows(IllegalMonitorStateException.class, () -> monitor1.getWaitQueueLength(guard));
  }

  public void testHasWaitersWithWrongMonitorThrowsIMSE() {
    Monitor monitor1 = new Monitor();
    Monitor monitor2 = new Monitor();
    FlagGuard guard = new FlagGuard(monitor2);

  // TODO: Test enterIf(Guard, long, TimeUnit).
  // TODO: Test waitFor(Guard, long, TimeUnit).
  // TODO: Test getQueueLength().
  // TODO: Test hasQueuedThreads().
  // TODO: Test getWaitQueueLength(Guard).
  // TODO: Test automatic signaling before leave, waitFor, and reentrant enterWhen.
  // TODO: Test blocking to re-enter monitor after being signaled.

   * designed primarily for use in monitoring of the system state.
   */
  public boolean hasWaiters(Guard guard) {
    return getWaitQueueLength(guard) > 0;
  }

  /**
   * Returns an estimate of the number of threads waiting for the given guard to become satisfied.