Worked on the apache/kafka repository to improve the stability of Kafka’s unit tests following a Mockito upgrade. Focused on refactoring the deleteRecords test stub to use partition-based matching, this approach addressed issues caused by default return values in newer Mockito versions. By aligning test stubs with data partitioning logic, the work reduced test flakiness and maintenance overhead, resulting in a more resilient and maintainable test suite. Leveraged Java, Mockito, and unit testing best practices to enhance continuous integration reliability, enabling faster developer feedback and more dependable releases. The contribution centered on bug fixing and test infrastructure rather than feature development.