In the ideal setting no, you will have strong contractual boundaries and these will all be tested by integration tests that live in a separate layer - but not on every commit of the sub projects - it will happen less frequently and roll up many changes across multiple subprojects together and test them all at once. Yes you lose some granularity and immediacy but it solves the scaling problem.

Everything works like this in the end at some level. I assume people with monorepos don't retest their project on every Linux kernel commit - it's pointless, you are never going to run against exactly that commit. But you will do it when you do upgrade Linux versions, etc.