Accessibility testing

The goal is for the entirety of the EUI docs site to be run through axe. As of #2569, all of the Guidelines pages are tested and the plumbing is in place to add the rest.

What is axe?

axe is an "accessibility engine for automated Web UI testing". Automated tests cover ~30% of accessibility requirements but, ~60% of accessibility bugs are caught by automated tests. So, though it can't replace manual testing, it's a great baseline for all of our components to meet.

How to run the tests?

• start-test-server-and-a11y-test runs the test suite against the entire docs site and manages it's own local server for it.
• test-a11y can be used if you want to run it against your dev server (assumed to be `http://localhost:8030).

How to run it against 1 component?

Though it's not setup to be run this way, there are two ways to do it.

The recommended route is to install the axe addon (for Chrome or Firefox). Navigate to any page and run the analyzer from your browser's dev tools. This will return the same* results to you while also giving you some convenience utilities like highlighting the exact element that's failing.

Not as nice of a experience though potentially more direct, in scripts/a11y-testing.js you can modify the list of component pages return from docsPages() to run only one file. But remember not to check in these changes!

* It might not actually be the same in a couple cases (e.g., we've disabled some rules or a recent update that was pushed to the addon but we haven't updated yet) but it will generally be more strict that we are so you should never see something in CI that you can't see in the addon.

Deconstructing an error message

`[${id}]: ${description}
  Help: ${helpURL}
  Elements:
    - ${nodePath}
`);

All error messages follow this same structure:

• The id will always map to the same description and helpURL.
• The description will give a one sentence explanation of the problem.
• The helpURL will take you to axe's documentation about the problem. The documentation is generally pretty strong and will walk you through different possible problems and remediation steps.
• The nodePath is the only thing that doesn't come directly from axe and is an attempt to lead you to the element that's triggering an error. (See printResult() in scripts/a11y-testing.js to see exactly how it's generated.)

The set of failures for each page will be denoted by a line with the URL of the page being tested.