Now that we have a code base written in a testable way, let's automate those tests so that we do not have to perform them manually and can continue to code and refactor with ease.

If you look at the spec/viz_spec.js file, you will note some common patterns when unit testing. The following code is written with a JavaScript unit-testing framework called Jasmine and leverages Karma to execute the tests. You can learn more about the Jasmine syntax, assertions, and other features at http://jasmine.github.io/1.3/introduction.html.

The bootstrap project has everything you need to start testing quickly.

The first step is to start our Karma test runner with this line of code:

node_modules/karma/bin/karma start

This runner will watch every edit of the viz.js file or the viz_spec.js file. If any changes are detected, it will automatically rerun every test suite and provide output on the console. If all the tests pass, then the output will be all green. If something fails, you will receive a...