Finn Plum expanded test coverage for the countbits intrinsic in the llvm/offload-test-suite repository, focusing on comprehensive validation across multiple integer types. He developed dedicated test files for 16-bit, 32-bit, and 64-bit signed and unsigned variants, ensuring cross-platform consistency and improved reliability. By leveraging HLSL and YAML, Finn applied his skills in shader development and testing to enhance the suite’s regression protection and contribute to CI stability. His work demonstrated a solid understanding of C/C++ testing practices and test harnesses, addressing the need for robust cross-type validation and laying groundwork for more reliable feature verification in future development cycles.