monitor.leave();
    thread1.assertPriorCallReturns(enterWhen());
  }

  public final void testEnterWhen_alreadyOccupied() throws Exception {
    TestGuard guard = new TestGuard(true);
    thread2.callAndAssertReturns(enter());
    thread1.callAndAssertBlocks(enterWhen(), guard);
    thread2.callAndAssertReturns(leave());
    thread1.assertPriorCallReturns(enterWhen());
  }