Downstream testing for language pacakge managers, it's buildable but perhaps not fundable?

https://nesbitt.io/2026/03/01/downstream-testing.html

Downstream Testing

Most library maintainers have no way to test against their dependents before releasing.

Andrew Nesbitt
@andrewnez can I point cargo-semver-check? It is not *exactly* what you are talking about here, but I think it helps a lot with that problem and allows to push it back upstream with less stuff to run.
@Di4na if we had that in every other language, we’d be in a much better place
@andrewnez so funnily enough, iirc they mentionned they had a prototype for python and ruby iirc... but no funding to do all the work to productivize it