public void testSumManhattan() {

        PuzzleState test1 =
            new PuzzleState('5','2','7','8',' ','4','3','6','1');

        // Here is test1:
        //          +---+---+---+
        //          | 5 | 2 | 7 |
        //          +---+---+---+
        //          | 8 |   | 4 |
        //          +---+---+---+
        //          | 3 | 6 | 1 |
        //          +---+---+---+

        PuzzleState test2 =
            new PuzzleState('5','6','7','4',' ','8','3','2','1');

        // Here is test2:
        //          +---+---+---+
        //          | 5 | 6 | 7 |
        //          +---+---+---+
        //          | 4 |   | 8 |
        //          +---+---+---+
        //          | 3 | 2 | 1 |
        //          +---+---+---+

        assertTrue(test1.sumManhattan() == 16);
        assertTrue(test2.sumManhattan() == 24);
    }