What is the most important behavior, which is not yet implemented?
A game isn't much fun if you can't control it. As the next step, let's make it possible for the player to move the falling tetrominoes left, right and down.
It's time to write your own tests. Here are some example test names, which should be enough to cover all the corner cases:
- a falling tetromino can be moved left
- a falling tetromino can be moved right
- a falling tetromino can be moved down
- it cannot be moved left beyond the board
- it cannot be moved right beyond the board
- it cannot be moved down beyond the board (will stop falling)
- it cannot be moved left through other blocks
- it cannot be moved right through other blocks
- it cannot be moved down through other blocks (will stop falling)
Remember to follow the three laws of TDD and not write more than one failing test before making it pass.
Also remember to follow the red-green-refactor cycle. In particular, run each test immediately after writing it, so that you will see it fail. That's important for "testing the test", to ensure that the test is testing what you think it's testing, and that the failure message is understandable.