@Test
 public void testGettingMarkThatShouldBeEmptyInMiddleAndReturningAsAString() {
   TicTacToeGUI board = new TicTacToeGUI();
   board.setMark(0, 0);
   board.setMark(2, 2);
   assertEquals(" ", board.getMarkInString(1, 1));
 }
 @Test
 public void testGettingMarkInBottomLeftAndReturningAsAString() {
   TicTacToeGUI board = new TicTacToeGUI();
   board.setMarkO(2, 0);
   assertEquals("O", board.getMarkInString(2, 0));
 }
 @Test
 public void testGettingMarkInTopLeftAndReturningAsAString() {
   TicTacToeGUI board = new TicTacToeGUI();
   board.setMark(0, 0);
   assertEquals("X", board.getMarkInString(0, 0));
 }