I have used the Jest and Mocha frameworks for automated testing of code, but as Jest is the preferred option for the CLI tools, I am tending toward that. I have 2 public projects in GitHub which demonstrates testing in Jest. I am preparing for an internal presentation on how to integrate testing into a legacy project, because I've seen the value of it over the past year and I want to see more of it in professional projects. Since adding comprehensive automated testing into our CI/CD pipeline around a business critical section of an app, we've caught errors that would normally end up being reported by the client or manual testing. I've also used E2E frameworks like puppeteer, nightwatch and a little Selenium.