Frontend headless browser testing with Puppeteer

A big cost area in testing is manual user interface testing. Therefore, a wide range of tools have been developed to automate running tests at the HTTP level. Selenium is a popular tool implemented in Java, for example. In the Node.js world, we have a few interesting choices. The chai-http plugin to Chai would let us interact at the HTTP level with the Notes application, while staying within the now-familiar Chai environment. 

However, for this section, we'll use Puppeteer (https://github.com/GoogleChrome/puppeteer). This tool is a high-level Node.js module to control a headless Chrome or Chromium browser, using the DevTools protocol. That protocol allows tools to instrument, inspect, debug, and profile Chromium or Chrome. 

Puppeteer is meant to be a general purpose test automation tool, and has a strong feature set for that purpose. Because it's easy to make web page screenshots with Puppeteer, it can also be used in a screenshot service.

Because...