I spent 3 years getting a Ruby codebase to 100% branch coverage running locally in a few minutes (I wasn't just looking at coverage, I was also profiling for slow tests). Found a few bugs ofc having to read through code so carefully. The value was having a layer of defence while refactoring, if some unrelated test failed it implied you missed impact of your change. It also helped people avoid the issue of making changes to an area of code with no testing, where existing tests act as docs (which execute, so won't go stale as easily) & make it easier for new code to write new tests building on existing tests

This codebase was quick to deploy at Microsoft. We'd rollout every week. Compared to other projects that took months to rollout with a tangling release pipeline

Anyways I left for a startup & most of this fast moving team dissolved, so the Ruby codebase has been cast aside in favor of projects with tangling release pipelines

https://techcommunity.microsoft.com/blog/adforpostgresql/how...