This is a separate section from the CONTRIBUTING.md document. It will contain a small guide on testing things you wish to implement for bugs & other issues, which is crucial to do before submitting a Pull Request to the repository.
Can't work without tools, right? Here's a list of simple but effective tools you can use for testing & fixing bugs.
Atom - One of the most prominent text editors used by MAS contributors, Atom has many tools & features that allow for efficient and clean work on files that are being edited. It even has tools for fixing merge conflicts.
Ren'Py - Ren'Py is required for running the source code outside of a released version, which is needed for testing things you wish to add for bugs & other issues.