From 40 Minutes to 4 With Tests Parallelization - FastRuby.io | Rails Upgrade Service

How we cut a test suite time from 40 minutes to 4 by upgrading Ruby/Rails, fixing slow tests, and enabling parallelization, dramatically improving developer experience and CI costs.Last month, we finished a big upgrade for a client. The client had 2 main pain points for their app. The first one was that they were using Rails 2.3 LTS with Ruby 2.5. The next big issue was that the test suite took 40 minutes to run, blocking engineers from merging code into the main branch, and also slowing down the whole feedback loop for every code change. After finishing the upgrade (we got the application to Rails 8.1.1 and Ruby 3.4.7), we focused our attention on improving the test’s speed and we reduced the time it took to run the whole test suite (over 10k tests) from 40 minutes to around 4!.