@Test
    public void testHash() {
        int[][] ints = {
                {1, 2, 3},
                {4, 6, 7},
                {8, 9, PuzzuleNode.EMPTY}
        };
        Node node = new PuzzuleNode(ints, 2, 2);
        Set<Node> hashSet = new HashSet<>();
        hashSet.add(node);
        hashSet.add(node);
        Assert.assertTrue(hashSet.size()==1);
    }