Developed and delivered an end-to-end fallback sink testing feature for the numaproj/numaflow repository, focusing on the MonoVertex pathway. The work involved creating a new test case and configuration using Go and YAML to simulate primary sink failures and verify that messages are correctly routed to a fallback sink. This approach enhanced the system’s ability to validate failure recovery and improved the robustness of the sink pipeline in production-like scenarios. Leveraging skills in configuration management, end-to-end testing, and system testing, the contribution expanded test coverage and reduced the risk of data loss during sink failures without introducing any bug fixes.