In frontend work, testing can be a tricky thing to do. You can unit test, but there are so many other variables. Browser testing is a powerful, but hard to automate tool. Emil Ong talks about how he used CircleCI to automate his browser tests.
Progressive enhancement is a touchy subject. It can be hard to discuss dispassionately because, like accessibility, it’s often framed as an issue of empathy and compassion. Nolan Lawson dives into progressive enhancement and some of it's finer points.