@Override
    public void add(Object task, boolean priority) {
        checkNotNull(task, "task can't be null");

        if (priority) {
            priorityQueue.add(task);
            normalQueue.add(TRIGGER_TASK);
        } else {
            normalQueue.add(task);
        }
    }
@Test(expected = NullPointerException.class)
    public void add_whenNull() {
        operationQueue.add(null, false);
    }