Xinyi Yu focused on enhancing the robustness of Spark’s Dataset API CoGroup functionality in the apache/spark repository by expanding its test coverage. Using Scala and Apache Spark, Xinyi developed comprehensive tests to address complex key types, null keys, and empty datasets, targeting edge cases that could cause regressions in data processing pipelines. The work involved close collaboration with contributors across teams and emphasized regression safety by validating changes through Spark’s continuous integration system. Although no production features were released, the depth of testing improved code quality and reliability, ensuring that future changes to the CoGroup path are safer and more predictable.