Yes. For example, most CRUD apps are like this almost by definition. It's more common for domain logic to be fairly simple and smeared across multiple systems

Yes. For example, most CRUD apps are like this almost by definition. It's more common for domain logic to be fairly simple and smeared across multiple systems and languages, though - e.g. some is in SQL, some is in a separate microservices, some is in module A and some is in module B. In either case unit tests end up being mimetic tests: assert derp == derp.