https://arran4.github.io/blog/tags/mapfs/Recent content in mapfs on Arrans Technical blogHugo -- gohugo.ioentechnicalblog123@arran4.com (Arran Ubels)technicalblog123@arran4.com (Arran Ubels)Arran Ubels. This work is licensed under a <a rel="license" href="http://creativecommons.org/licenses/by-sa/4.0/">Creative Commons Attribution-ShareAlike 4.0 International License</a>.Fri, 14 Aug 2026 00:00:58 +0000https://arran4.github.io/blog/post/2026/033-testing-fs-with-mapfs-mockfs/Fri, 14 Aug 2026 00:00:58 +0000technicalblog123@arran4.com (Arran Ubels)https://arran4.github.io/blog/post/2026/033-testing-fs-with-mapfs-mockfs/When building tools in Go that interact heavily with the file system, having a solid strategy for testing those interactions is critical. Direct coupling to os functions like os.MkdirAll or os.WriteFile makes testing cumbersome and slow. In this post, I want to detail how I approach this by designing minimal file system interfaces and using in-memory implementations like MapFS and MockFS for tests. Why This Matters in the Era of Agentic Coding Before diving into the code, it&rsquo;s worth highlighting why robust, abstract testing environments are becoming even more critical today.