Contributed to the nestjs/nest repository by building robust audio processing test infrastructure and enhancing backend validation logic. Focused on expanding unit and end-to-end test coverage for audio transcoding, introducing a mock BullModule to decouple tests from Redis while enabling true integration testing in CI environments. Improved test reliability by refining concurrency and timeout settings, and updated CircleCI configurations to support Redis-based workflows. In backend validation, refactored the ValidationPipe to better handle built-in JavaScript types, centralizing type management and adding targeted tests to prevent regressions. Worked primarily with TypeScript, Jest, and NestJS, emphasizing maintainability and test-driven development practices.