Worked on the GreenCityMVP21 repository, delivering comprehensive unit-test coverage for core filtering specifications in Java using JPA Criteria API and Mockito. Developed and documented two robust test suites for HabitFactSpecification and ShoppingListItemSpecification, addressing ID and content filtering, related entity joins, null content handling, and multi-criteria combinations. This approach strengthened the reliability of data-layer filtering logic for habit tracking and shopping list workflows, reducing the risk of regressions and enabling safer, faster feature iterations. Emphasized test-driven development and code quality, with clear test documentation to guide future maintenance and ensure consistent, high-confidence backend development practices throughout the project.