done new isBroken on Sudoku level 
junit assetTrue and assetFalse are very effective

   @Test
    public void testIsBroken() {

        Sudoku s = new Sudoku();
        s.setMembersByGroup(1, 1, 2, 3, 4, 5, 6, 7, 8, 8);
        s.show();
        assertTrue(s.isBroken());
        s.setMembersByGroup(1, 1, 2, 3, 4, 5, 6, 7, 8, 9);
        s.show();
        assertFalse(s.isBroken());
    }
 --- Sudoku 9x9 --- (start)
 1 2 3 4 5 6 7 8 8
 . . . . . . . . .
 . . . . . . . . .
 . . . . . . . . .
 . . . . . . . . .
 . . . . . . . . .
 . . . . . . . . .
 . . . . . . . . .
 . . . . . . . . .
 --- Sudoku 9x9 --- (end) known cells count: 9
 123456788_000000000_000000000_000000000_000000000_000000000_000000000_000000000_000000000
 xxx It's broken! xxx

 --- Sudoku 9x9 --- (start)
 1 2 3 4 5 6 7 8 9
 . . . . . . . . .
 . . . . . . . . .
 . . . . . . . . .
 . . . . . . . . .
 . . . . . . . . .
 . . . . . . . . .
 . . . . . . . . .
 . . . . . . . . .
 --- Sudoku 9x9 --- (end) known cells count: 9
 123456789_000000000_000000000_000000000_000000000_000000000_000000000_000000000_000000000
 ...still in good shape