Nicolas Osborne expanded test coverage for the Dune Plugin System in the ocaml/dune repository, focusing on validating plugin extensibility and packaging workflows. He developed a blackbox test harness using OCaml and Shell scripting, setting up a reproducible multi-package project that loads plugins and verifies dune-site and dune package interactions end-to-end. This approach exercised the full packaging and usage flow, enabling detection of regressions in plugin-based workflows and strengthening CI reliability. By integrating build systems, package management, and testing expertise, Nicolas ensured that future changes to the site plugin mechanism could be confidently validated, supporting safer extension points for users.