Brage Hagen refactored and strengthened the Temporal API calendar tests in the tc39/test262 repository, focusing on improving both robustness and maintainability. He consolidated and reorganized calendar-related test cases, clarified file naming conventions, and restructured test groupings to streamline maintenance and reduce CI overhead. By implementing strict validation logic in JavaScript, he ensured that invalid calendar parameters reliably trigger RangeError or TypeError, thereby enhancing regression protection for calendar features. His work expanded test coverage for the Temporal API, leveraging skills in API development, JavaScript, and automated testing to deliver a more reliable and maintainable test suite for future development.