[EvanPlaice]

"wanted the title to be intentionally provocative"

Click bait adds no value to the discussion.

There's no either/or when it comes to karma/mocha. As the commenters above mentioned, it's best to use both. Mocha for quick unit testing, karma for in-browser testing.

In-browser testing can be automated to run on a wide range of browsers and platforms using integration tools such as Browser Stack.

By faking the DOM, you remove nerf the greatest advantage of client-side integration testing. Checking functionality under realistic circumstances.