Add Tests

Add test cases so that further refactoring does not break what you already achieved.

A basic setup using pytest has already been established on the add-tests branch, which you can build upon.

Before you do that:

1. Finish the current refactoring cycle
2. Merge refactoring → main
3. Merge main → add-tests

Finish by doing:

• Add the run of pytest as a dedicated CI-Jpb