Added last tests, reached 100% coverage

The MVP 1 (and all its functionnalities) is now finished. It's time to get the Tkinter to work to finish MVP 2 in the same time. Then, the remaining hours of the Game Jam will be used to add bonus game mechanics in the MVP 3.

requested review from @paul-emile.delavaud

assigned to @paul-emile.delavaud

mentioned in commit 3562ffe5

merged