Thanks for the response, Vikas, it's really appreciated.
I've tried hunting down where I might be logged in postgres or jbilling-test, but haven't been able to diagnose where. When I access postgres admin (pgAdmin), it has that "red x" covering localhost, which contains the jbilling-test database, so I'm not locking it up as a resource. I exit the postgres admin tool prior to running grails prepare-test.
I'm clueless as to where (or even how) I'm logged in. Any suggestions?