Validate WEB_FEATURES.yml

[jugglinmike]

For every pull request, verify that the WEB_FEATURES.yml file is internally consistent and that the pull request does not reduce the number of tests associated with a given classifier.

Failing for any reduction in the number of matched tests is intended to alert contributors during file renaming operations. This failure will need to be ignored when tests are simply deleted, and this could potentially become a distraction for maintainers. However, test deletion has historically been so rare that spurious failures are not expected to be common enough to substantively interfere with routine maintenance.

[ptomato]

However, test deletion has historically been so rare that spurious failures are not expected to be common enough to substantively interfere with routine maintenance.

I think the main place where this would come up is when moving tests out of staging, into the main tree. They might get merged into existing tests. I don't actually know if the classification applies to the staging folder in the first place, so maybe this isn't a problem.

[jugglinmike]

I think the main place where this would come up is when moving tests out of staging, into the main tree. They might get merged into existing tests. I don't actually know if the classification applies to the staging folder in the first place, so maybe this isn't a problem.

That's a good call-out! We haven't classified tests in staging, so fortunately those kinds of moves won't be an issue.