Yandi Ma developed a comprehensive test suite for the necysc_app core models in the fullstackatbrown/project-necysc repository, focusing on backend development with Django and Python. The work involved implementing tests to verify Applicant model default values, data creation paths, and the singleton-like behavior of the GlobalData model, as well as validating the initialization of cost attributes. By introducing a new test script and integrating it into the codebase, Yandi enhanced regression safety and clarified data contracts. This effort improved the reliability of core data structures, supported safer refactoring, and facilitated faster onboarding for new developers through increased test coverage.