I recently wrote a patch for Grails to support dateCreated and lastUpdated when using mockDomain in unit tests.
This patch has now been applied to 1.2-SNAPSHOT.
http://jira.codehaus.org/browse/GRAILS-4540
The mockDomain method makes it possible to test code that uses GORMs dynamic methods, without having to use a real database.
IBM Developerworks has a great article on mock testing in Grails here.