How to resolve Error in karma unit testing: Can not load "Chrome"..?

I am getting my head around karma unit testing, I just installed this for my angular app in osx:

# Install Karma:
$ npm install karma --save-dev

# Install plugins that your project needs:
$ npm install karma-jasmine karma-chrome-launcher --save-dev

My karma config is generated with karma init and contains this:

 plugins: [
            'karma-chrome-launcher',
            'karma-jasmine'
        ],

However when I run karma start I get:

 Can not load "Chrome", it is not registered!
  Perhaps you are missing some plugin?

How can I fix this?