It turns out that yarn intentionally supports these! The jest repository depends on that feature, so I added it as a regression/smoke test target.
Unfortunately as my comment notes, it isn't a proper end-to-end test, so there are failures it would not catch: jest has a single script at the repository's root for transpiling all packages, but I couldn't find a way to leverage that for individual packages.
It turns out that yarn intentionally supports these! The jest repository depends on that feature, so I added it as a regression/smoke test target.
Unfortunately as my comment notes, it isn't a proper end-to-end test, so there are failures it would not catch: jest has a single script at the repository's root for transpiling all packages, but I couldn't find a way to leverage that for individual packages.