Document a workflow for axe accessibility testing

[calebeby]

It would be nice if we could interject accessibility tests at different points in our tests.

Chances are, this would work out of the box (I have not tried it):

https://github.com/dequelabs/axe-core-npm/tree/develop/packages/puppeteer

We should check if it works, add an example using it (also maybe add the workflow to the README), and decide whether it makes sense to pull in that library to Test Mule to make it easier to use.

[calebeby]

@axe-core/puppeteer is definitely still an option, but I tried out @wordpress/jest-puppeteer-axe which adds Jest assertions which is a little nicer.

await expect(page).toPassAxeTests();

[calebeby]

FWIW @wordpress/jest-puppeteer-axe is a very small wrapper around @axe-core/puppeteer, so it is probably possible for us to make our own wrapper that allows passing live element references in the error messages which would be probably more helpful for debugging.

https://github.com/WordPress/gutenberg/blob/trunk/packages/jest-puppeteer-axe/src/index.js

[calebeby]

#494

Released in v2.2.0