Testing your code well is hard, and it can be easy to neglect. You’ll be glad you didn’t though when you have to change the implementation of a feature without your users noticing anything, except maybe a performance bump. Let’s go through how we can use and modify existing tests to allow a change in code that you can be confident will work when you get to production. https://chrisherring.co/posts/put-your-tests-to-good-use-refactor-with-confidence