My 12-year development career has been on one large enterprise web application under continual development. Our team, averaging 20 full-stack developers, has built what now amounts to 3 million lines of code. While we follow best practices like test automation with continuous integration and upgrade to newer frameworks as we can, there is a unique set of challenges when testing and upgrading front-end behavior with JavaScript frameworks on a large project. We’ll start with my team’s testing strategies as a case study to learn from what we did right and where we stumbled. What could we have done differently? What are the best practices for front-end testing a large web application?