Finally, we can check whether X's turn comes after O played.
There's nothing to do to fulfill this test and, therefore, the test is useless and should be discarded. If you write this test, you'll discover that it is a false positive. It would pass without changing the implementation; try it out. Write this test and if it is successful without writing any implementation code, discard it.
The source code can be found in the 02-next-player branch of the tdd-java-ch03-tic-tac-toe Git repository at https://bitbucket.org/vfarcic/tdd-java-ch03-tic-tac-toe/branch/02-next-player.