It works for user facing documentation too. There are actually pretty good reasons for this - e.g. you can use the test to autogenerate up to date screenshots with playwright to put in the documentation.

I'm pretty convinced that there should be a single source of truth for specifications, tests and documentation but I think the industry will take a while to catch up to this idea.

I built a testing library centered around this (same as my username) but it's hard to get people to stop writing unit tests :)