Added a short section to pre-commit and testing.

CONTRIBUTING.md

@@ -12,6 +12,9 @@ Each chapter of the book has as a separate Markdown file in the root directory (
 If you want to fix typos or add material, edit these chapters directly in the root directory.
 Please do not make edits to the `README.md` file as this file will be automatically generated by running the `build.py` script.
 
+If you install [pre-commit](https://pre-commit.com/), formatting and building will be done automatically for every commit.
+pre-commit can be installed from pip via `pip install pre-commit` and activated with `pre-commit install` in the repository.
+
 ## Building the Book Locally
 
 To preview the changes that you make to the book:
@@ -75,3 +78,13 @@ To preview the changes that you make to the book:
 
 10. Be prepared to make additional changes if requested by the maintainers.
 
+## Testing
+
+CP-SAT is under rapid development, and its behavior can change from time to time.
+Therefore, while it is not mandatory, it is highly appreciated if code snippets are
+converted into simple test cases. These test cases do not need to be complex;
+even detecting syntax errors when CP-SAT changes is valuable.
+All test cases will be automatically run every week against the latest version
+of CP-SAT to ensure that the code snippets remain valid.
+
+