GH Actions tests -- what are they testing?

Hey @dgrebb, I was looking at the GH Actions test output and saw that the `npm run sanity-test`s are detecting mismatch errors. My question is -- what exactly are we testing by running these? What kind of error would these GH Actions tests find?


Thanks!

Start with the GitHub Actions test output and the `npm run sanity-test` command mentioned in the issue. Determine what the sanity tests exercise and what mismatch errors represent, then document that purpose and the kinds of failures they catch. Done means a contributor can understand the test's scope from the documentation.

Written by the indexing model from the issue text.