Worked on the typelevel/cats repository to enhance the reliability and clarity of the NonEmptyList data structure by introducing doctest-based tests for the forall and exists methods. Leveraged Scala and functional programming principles to create documentation-driven tests that both demonstrate and verify expected behaviors. This approach improved maintainability by ensuring that documentation and code remain synchronized, reducing the risk of regressions during future refactors. The addition of these tests also supports faster onboarding for new contributors and lowers long-term support costs. Focused on testing and documentation, the work contributed to a more robust and user-friendly open-source codebase.