Now, we should make sure that players are changing. After X is finished, it should be O's turn, then again X, and so on:
@Test
public void givenLastTurnWasXWhenNextPlayerThenO() { ticTacToe.play(1, 1); assertEquals('O', ticTacToe.nextPlayer()); }
If the last turn was played by X, then the next turn should be played by O.