@Test
    public void testNextSteps_normal_topLeft() {
        int[][] ints = {
                {PuzzuleNode.EMPTY, 1, 2},
                {3, 4, 6},
                {7, 8, 9}
        };

        List<Node> nextSteps = new PuzzuleNode(ints, 0, 0).nextSteps();

        assertThat(nextSteps.toString(),
                is("[[3, 1, 2][-1, 4, 6][7, 8, 9], [1, -1, 2][3, 4, 6][7, 8, 9]]"));
    }