Tanmat contributed to the JoyOfCodingPDX/KatasSummer2025 repository by developing a Diamond Pattern Printing feature in Java, introducing a print method and line-building utilities to render centered diamond shapes. They enhanced test coverage with targeted unit tests, including cases for specific inputs like 'B', ensuring reliable output and robust validation. Tanmat also implemented repository write-access verification and improved author metadata to support collaboration and documentation. In the following month, they focused on code quality by cleaning up the Diamond test suite, removing redundant cases to reduce flakiness and improve CI reliability. Their work emphasized Core Java and disciplined unit testing practices.