Even if the Container runs in-vm, executing the testcase in 'local' mode does not make the test run inside the container, that only makes it run on the same classpath. Your then not really looking up resources from inside the deployment, but rather as a normal client. The result might not be exactly the same.
So to repeat myself from IRC (for anyone following along here):
"We can use this as an opportunity to clean up and document as we go."
When I hear "local", and this may just be my EJB background, I think it's in the context of VM/process. I'm still wondering why GFv3 tests shouldn't be executed as clients, but rather from inside the container, but more confusing is the naming to me.