Here, I've tried good tests with TDD standards. Actually, I was inspired by the Test-Driven Development book by Viktor Farcic and Alex Garcia.

This game has been played by everybody. You only need to wait your turn and win. As you know, X starts and then O continues. It is possible to win by going vertical, horizontal, or diagonal. That's why I tried to use every winning structure.

I attempted to write a tic-tac-toe game with TDD. I completed that version with 100 percent coverage. Win, draw, no winner, outside the board, occupied board, vertical, horizontal, and diagonal wins. The test is written with JUnit5.