public abstract void clear();
@Test
    public void clear() {
        final PriorityQueue<Integer, String> queue = createQueue();
        queue.push(0, "1");
        Assert.assertTrue(queue.size() > 0);
        Assert.assertFalse(queue.isEmpty());
        queue.clear();
        assertEquals(0, queue.size());
        Assert.assertTrue(queue.isEmpty());
        Assert.assertNull(queue.peek());
        Assert.assertNull(queue.pop());
    }