As with almost everything else done in the TDD fashion, implementation is fairly easy:

private int turn = 0;
...
public String play(int x, int y) {
  checkAxis(x);
  checkAxis(y);
  lastPlayer = nextPlayer();
  setBox(new TicTacToeBean(++turn, x, y, lastPlayer));
  if (isWin(x, y)) {
    return lastPlayer + " is the winner";
  } else if (isDraw()) {
    return RESULT_DRAW;
  } else {
    return NO_WINNER;
  }
}