Some google-cloud-* libraries have both gRPC (gax) transports and HTTP transports. Logging, Datastore, Error Reporting, Pub/Sub at least. The clients generally try to use gRPC unless there's an ImportError (no gRPC support) ,or it's explicitly disabled by google.cloud.environment_vars.DISABLE_GRPC or a constructor argument to the client.

As far as I can tell most system tests just instantiate a client, so the tests only use one of these transports. On the CI systems gRPC is supported and so I think the HTTP paths are less tested.

@jonparrott asked about this in #3386, it seemed a reasonable thing to give some thought to, so just wanted to create a discussion tracking issue.

I think this would be somewhat straightforward to do with nox, so main question is probably whether it's worth doing. Making the CI build slower is probably the biggest negative.