Thanks to headless browsers—browsers that don't render to a display interface—both E2E and unit tests can be run from the server. However, we should also test these unit tests in a real browser, as there might be inconsistencies between NodeJS (which uses the V8 JavaScript Engine), and other browsers like Firefox (which uses the SpiderMonkey engine), Microsoft Edge (which uses the Chakra engine), and Safari (which uses the Nitro engine).
To test on real browsers and devices, we can use a different test runner called Karma (https://karma-runner.github.io/2.0/index.html).
