Add examples of how to test gRPC methods

[nkhil]

I'm not sure if this should be in 'issue' so feel free to close. I'm hugely thankful for this repo, as I was struggling to find a working example of a simple grpc server and client.

Having put together a simple grpc repo myself, I am now struggling to come up with a way to test this setup. I'd like to be able to get the server running, then invoke the client and assert against the response on the client side.

Any resources on how I can do this please?