Finally, there is the last possible winning condition to tackle:
@Test public void whenPlayAndBottomTopDiagonalLineThenWinner() { ticTacToe.play(1, 3); // X ticTacToe.play(1, 1); // O ticTacToe.play(2, 2); // X ticTacToe.play(1, 2); // O String actual = ticTacToe.play(3, 1); // X assertEquals("X is the winner", actual); }
The player wins when the whole diagonal line from the bottom-left to top-right is occupied by his pieces.