Hi Helmut,
at the moment I devote all my time and energy to the Spock core. That's why I have yet to investigate how Spock could be used to test Grails applications. If you could provide some feedback, ideas, or code, that would be great! Don't hesitate to post your questions or findings to the Spock forum:
http://groups.google.com/group/spockframework (anyone can post,
no Google account required)
Cheers,
Peter