Since Gerrit change 302944 the category Category:UnitTestsList extensions is no more a reliable way to obtain a census of unit tested extensions. I plan to create two categories Category:Unit tested extensions and Category:Unit tested skins (or not for the latter?). I’m not sure if a parameter "phpunit = yes" should be added in Template:Extension or if I only write category in the wikitext of the page; probably the first option I guess. Any thoughts?
Topic on Talk:Continuous integration/Flow
Can you explain why you want such a category? Just checking whether an extension has tests doesn't mean much...we'd really want coverage statistics. There's also that we run core's structure tests on many extensions, which adds some coverage as well.
I find it is useful to create basic statistics about extensions quality, I did last year some stats about extensions (here – I very badly referenced this page, a bit better now), and extensions with unit testing (even basic) is an indicator about "good quality". I aggree stats about code coverage is better to have finer statistics, but a thredhold "have or not unit tests" give a first approximation -- which could be emphased in Template:Extension for instance to show quality: e.g.
| unit tests | registration | git | i18n | i18n-qqq | user doc |
| ✓ | ✓ | ✓ | ✓ | ✗ | ✗ |
It would be quite easy to read and understand for somebody searching for an extension (the more "check" there is the better it is) and quite easy to maintain on MediaWiki.org (once an extension has created unit tests it has a "check" forever), and it could encourage extension developers to improve the quality. Obviously I chosed some criteria here but it is open for discussion.