Automated testing

[jelmervdl]

This extension, specifically the InPageTranslation class, is becoming complex enough that things that fix one page break another. I also have pretty much lost oversight over what causes a performance regression, and how bad it is.

So I would very much love some automated testing on a bunch of simple and complex pages. Something that covers:

• Wikipedia (as a baseline)
• Some popular (including non-English) news sites
• Some dynamic web apps: Youtube, Twitter, Booking.com, Webmail?
• Known sites that break (or used to break) the add-on because they use custom elements or MutationObserver in a way that interfered with the add-on

I have no idea right now how to set this up. It would involve dealing with navigating (especially important for the dymamic web apps) and seeing how long it takes for the page to load, translate, and whether translation is complete.

Mozilla uses something called Mochitest for their version of the add-on, but I don't think they do any testing on real pages. I think I'd like to test on the live pages as the goal is to keep the add-on working with the websites as they are served now, not when I wrote the test.