Final considerations

Using TDD, we got a class with a constructor, five public methods, and six private methods. In general, all methods look pretty simple and easy to understand. In this approach, we also got a big method to check winner conditions: checkWinner. The advantage is that with this approach we got a bunch of useful tests to guarantee that future modifications do not alter the behavior of the method accidentally, allowing for the introduction of new changes painlessly. Code coverage wasn't the goal, but we got a really high percentage.

Additionally, for testing purposes, we refactored the constructor of the class to accept the output channel as a parameter (dependency injection). If we need to modify the way the game status is printed, it will be easier that way than replacing all the uses in the traditional approach. Hence, it is more extensible. In the test-last approach, we have been abusing the System.println method and it will be really tedious task if we decide to change...