Our Ruby on Rails System Tests Got 4 Times Faster With One Setting

Let me explain something right away: what I’m going to talk about is pretty unique to our application. If you don’t have an application like ours, then what I’ve written here might not help you. Our application is very big (3.8 million lines of Ruby), and has 10 years of history. If you skip to the end, and just apply the solution, it might not do anything for you. It could even make things worse! But, I hope that everyone can learn something from this story about how we made our tests faster.With that in mind, here's the story.