[shados]

It's becoming more and more popular not to use a browser for unit tests.

You do "pure" unit tests, which test most of the logic, computations and intention in nodejs, then rely on (usually just a few) E2E tests in selenium or whatever to make sure stuff actually work in the browser.

For example, in a standard React/Redux app with low amounts of legacy code, you can test almost all of the app's constructs in node and be very confident that everything works.

There's still a few places where Karma + Browser shine. Namely when something requires a unit test-style environment but is integration heavy. Think libraries abstracting browser details such as a rich text editor or a library like jQuery.