https://arran4.github.io/blog/tags/concurrency/Recent content in concurrency 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, 02 Oct 2026 11:55:00 +1000https://arran4.github.io/blog/post/2026/053-go-tests-treat-process-state-time-and-standard-io-as-dependencies/Fri, 02 Oct 2026 11:55:00 +1000technicalblog123@arran4.com (Arran Ubels)https://arran4.github.io/blog/post/2026/053-go-tests-treat-process-state-time-and-standard-io-as-dependencies/Filesystem access is only one form of hidden test dependency. The same problem appears when a unit test temporarily replaces process-wide state: 1old := os.Stdout 2os.Stdout = w 3defer func() { os.Stdout = old }() or: 1oldURL := APIURL 2APIURL = server.URL 3defer func() { APIURL = oldURL }() or: 1oldTimeout := defaultTimeout 2defaultTimeout = 10 * time.Millisecond 3defer func() { defaultTimeout = oldTimeout }() These tests can work, but they make otherwise local behaviour depend on global mutable state.