What Bitbucket learned from migrating its unit testing tool
Before Jest, our testing framework was a combination of different tools and helpers wired up together: Each of them serves a different purpose and is mandatory to write unit tests. The problem with that setup is that you need to maintain the custom integrations and this can cost you time and a lot of headaches. As you can guess, the complexity of this solution was evolving over time.
Those days are gone. We have more mature tools and, most importantly, more flexibility in how we want to provide and to run our unit tests. Thanks to the jsdom project we can run the code that works in the browser without a browser.