We just build and test everything every time. Maybe it costs us more $$$ on CI, but it costs far less in developer time. That being said, I mostly work at startups and larger companies will certainly cross a threshold where this isn't feasible.
>>> larger companies will certainly cross a threshold where this isn't feasible.
Nope. Worked at the largest US bank that happens to be mono repo. They had compute grids with thousands of cores running tests 24/7. It's not sizable compared to the costs of the developers writing and maintaining software.
Google, Twitter, and Facebook have open sourced their solutions to this. Bazel, Pants, and Buck. Each have some rough edges but I'm currently migrating a bunch of stuff to Bazel and the workflow and tooling for it is pretty amazing.
I feel this problem and I wonder, is there any ready-made solution for that?