	@Test
	public void checkerWorks() {

		int[][] test = {{0,0,0,0,0,0,0,0,0},
			{0,0,5,0,8,0,4,0,0},
			{0,4,6,7,2,9,0,5,1},
			{9,6,0,3,5,0,0,8,0},
			{0,0,0,0,6,0,9,3,5},
			{0,8,3,0,1,4,0,2,7},
			{1,7,0,5,0,0,2,0,3},
			{0,0,9,0,0,1,0,6,8},
			{0,5,4,2,3,8,7,0,0}};
		SDKBoard board = new SDKBoard();
		board.loadSimpleBoard(test);
		board.updateConstraints();
		assertTrue(HiddenSingleMaskFactory.isHiddenSingle(board.getSquare(5, 0), board));
	}