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 Puppeteer is controlling a real web browser, your user interface tests will be very close to live browser testing without having to hire a human to do the work. Because it uses a headless version of Chrome, no visible browser window will show on your screen, and tests can be run in the background, instead. A downside to this attractive story is that Puppeteer only works against Chrome. Meaning that an automated test against Chrome does not test your application against other browsers, such as Opera or Firefox.