Automated testing of web applications using JavaScript can provide confidence that changes and new installations do not break existing functionality. There are various types of tests, including unit, end-to-end, compatibility, and performance tests. Popular JavaScript testing tools include QUnit for unit testing, Selenium and Protractor for end-to-end testing, and PhantomJS for headless browser testing without a GUI. These tools can test JavaScript applications and allow writing tests in JavaScript when the application itself is also written in JavaScript.