// sleep() Tests
  public void testSleepNoInterrupt() {
    sleepSuccessfully(10);
  }

  public void testSleepSingleInterrupt() {
    requestInterruptIn(10);
    sleepSuccessfully(50);
    assertInterrupted();
  }

  public void testSleepMultiInterrupt() {
    repeatedlyInterruptTestThread(10, tearDownStack);
    sleepSuccessfully(100);
    assertInterrupted();
  }