Worked on the maths/moodle-qtype_stack repository over a two-month period, focusing on backend reliability and maintainability. Delivered a targeted refactor of PHPUnit test infrastructure by renaming and restructuring mock classes in API controller tests, which improved CI stability and eased future maintenance without altering production code. Addressed two bugs by resolving an undefined array key in healthcheck.php using PHP’s null coalescing operator and adding cache definitions to support unit test reliability. Applied best practices in PHP development, caching, and Moodle plugin patterns, resulting in more robust health checks, streamlined debugging, and enhanced test coverage for the STACK question type plugin.