"Knowing is not enough; we must apply. Willing is not enough; we must do."
The red-green-refactor technique is the basis of TDD. It is a game of ping pong in which we are switching between tests and implementation code at great speed. We'll fail, then we'll succeed and, finally, we'll improve.
We'll develop a Tic-Tac-Toe game by going through each requirement one at a time. We'll write a test and see if it fails. Then, we'll write a code that implements that test, run all the tests, and see them succeed. Finally, we'll refactor the code and try to make it better. This process will be repeated many times until all the requirements are successfully implemented. ...