If you only need this library during development, for instance to run your project's test suite, then you should add it as a development-time dependency: ...

Automated testing is an essential aspect of modern software development. It ensures the reliability of code and helps developers catch bugs early, making applications more sturdy and maintainable.

You don't have to modify CodeIgniter core files at all. You can write controller tests easily. Nothing is untestable, maybe. Well documented. codeigniter/ ├── application/ │ └── tests/ │ ├── ...