protoc-gen-go-grpc: add tests

[dfawley]

We don't currently have any tests in protoc-gen-go-grpc. We should add something simple at least:

1. Create a .proto file with streaming / unary RPCs.
2. Generate the .pb.go file(s) from it and commit it/them.
3. Write a test that does (2) and diffs the results with the committed file(s).

[Aditya-Sood]

hi @dfawley, can I pick this up?

[dfawley]

@Aditya-Sood ?

[Aditya-Sood]

thank you Doug, as suggested I will close the other issue and then pick this up

[miledxz]

@dfawley , Im looking what could be done here, but Annotate from protogen has been deprecated, do we need to take that in consideration too ?

[dfawley]

@zedGGs that seems unrelated. At the moment there are no tests, which means any changes made here have to be tested manually. If Annotate is deprecated then we should separately look into switching to whatever the alternative is, and having tests in place before making that change would help to ensure nothing is broken by the change.

[miledxz]

@dfawley I can take this one, if thats okey for you, I will add tests for unary RPCs, and if that goes well in pull request, I can also add tests for other RPCs streaming options,

feel free to assign me