Add tests

[KorribanMaster]

I appreciate all the work you put into this demonstration. I´m currently implementing my first tonic based application as a proof of concept and I was wondering how one could introduce unit and system tests for this example.
I have found this on stack overflow
https://stackoverflow.com/questions/69845664/how-to-integration-test-tonic-application
and read a little about tokio test but it is not obvious for me if this would be a good way or what other solutions there might be.
So in case this would be interesting content I would be interested.