Notes. It is about karma

karma.txt

Install karma-cli globally:
* npm i -g karma-cli

Set up the project:
* npm init
* npm i --save-dev karma
* karma init
   * Use the following responses when prompted:
       * Which testing framework do you want to use?
           * mocha
       * Do you want to use Require.js?
           * yes
       * Do you want to capture any browsers automatically?
           * phantomjs
       * What is the location of your source and test files?
           * app/assets/javascripts/**/*.js
           * spec/javascripts/**/*_spec.js
       * Should any of the files included by the previous patterns be excluded?
           * app/assets/javascripts/application.js
       * Do you wanna generate a bootstrap file for RequireJS?
           * yes
       * Do you want Karma to watch all the files and run the tests on change?
           * no

Set up test-main.js
* move into test directory
* add paths to files to be tested, e.g.
   *   paths: {
   *     // Dough components
   *     GlobalNav: ‘app/assets/javascripts/components/wpcc/components/ConditionalMessaging’
   *   }

Set up karma.conf.js
* move into test directory
* set config.set
   * basePath: ‘../‘,
   * frameworks: [‘requirejs’, ‘mocha’, ‘chai’, ‘sinon’],
   * files:
       * /path/to/test-main.js
       * [… {pattern: ‘javascripts/tests/*_spec.js’, included: false}]

To run
* ./node_modules/karma/bin/karma start spec/javascripts/karma.conf.js