Comment by kccqzy

If you understand how to evolve protobuf schema definitions, then you don’t really need testing. You instinctively know how the parser works when it is parsing data with a different schema from what it expects. And that’s a powerful thing. If your things break even when using protobuf then you don’t grok protobuf.

It’s probably not an exaggeration to say that being able to avoid tests between different systems who have different versions of the schema is a core goal of protobuf. Why? These two different systems are probably owned by different teams, and introducing explicit tests between different versions of them increases coupling between them.