When I run a test I get a few errors:

io.grpc.StatusRuntimeException: UNAVAILABLE: io exception

and

... Connection refused/[0:0:0:0:0:0:1]:63856

The tests work but the logs are full of these. Any advice on why?

O would expect that your gRPC client is trying to use some gRPC service that is unavailable during the test.

The issue is I'm just using protobufs, not gRPC

How have you setup the tests? This is a gRPC exception:

io.grpc.StatusRuntimeException