I was watching the pluralsight AngularJS fundamentals videos. The author didn't show how to configure the environment (Windows in my case) to be like in his videos, in particular node js and karma. I never used those, so I googled and found this detailed guide on how to set up node js and karma.
In my case, with angular-seed-master v1.2.4 (most up-to-date version), it was enough to download and install node.js, then open the windows command line and install karma with the default command (the last version is fine, no need to install 0.8.7 as the blog author suggested):
npm install -g karma
Then the tests work just fine.