@Test
 public void testDiagonalWinnerReturnsOneForSecondDiagonal() {
   int[] cell1 = {1, 1};
   int[] cell2 = {0, 0};
   board.setCellValue(cell1, 1);
   board.setCellValue(cell2, 0);
   assertEquals(1, GameState.DiagonalWinner(board));
 }
 @Test
 public void testDiagonalWinnerReturnsZeroForNoWinner() {
   assertEquals(0, GameState.DiagonalWinner(board));
 }