One thing I'd like to point out with testing frontend code is that typically, the test runners want to run in a browser window. This is great and makes perfect sense, but in the real world, automating your tests or quickly executing them with TDD can be a bit painful when a browser window wants to open every time your test suite runs. PhantomJS is an available headless browser that works perfectly in this kind of scenario. A headless browser simply means it's a browser that runs from the command line, in memory, with no actual interface (like a typical browser).

You can easily configure Karma to launch the test suite using PhantomJS instead of your browser of choice. When using PhantomJS as your browser, your tests execute behind the scenes, and only errors are reported. Here is a sample output of a test suite running with Karma using PhantomJS: