Automated testing functionality

Problem/Motivation

Currently, the module does not include any automated tests. This makes it difficult to ensure code stability, prevent regressions, and provide confidence when introducing new features or bug fixes. Automated testing will help maintain high code quality and simplify future development.

Proposed resolution

Introduce automated test coverage for the module. Depending on the type of logic covered, tests could include:
- **Unit tests** to validate isolated PHP classes and methods.
- **Kernel tests** to check integration with Drupal subsystems (entities, configuration, database).
- **Functional tests** to simulate user interactions, routes, and form submissions.
The initial goal is to establish a testing framework and add at least one basic test to serve as a reference for further coverage.

Remaining tasks

- Decide on the most relevant test type(s) for the module.
- Create a basic test class.
- Add more specific tests incrementally as needed.