In my experience, for regular libraries, you usually want to pin version ranges and not always use the latest of every library. But when the main business logic and a whole team is dedicated to one of the "service libraries", whose responsibility is it to make sure that the version stays up to date across other service libraries? Do you leave it up to the main host app? Do you allow a multitude of service library versions? Do you skip versioning all together? In microservices you have an opaque facade in the form of an API that makes this a non-issue. Perhaps you'd want some simulacrum of this in the form of IPC between service libraries?

Do you use some sort of contract based testing between service libraries? Put all integration testing in the host application?

It's not obvious to me what the best approach would be.