grails test-app -unit
or
grails test-app -integration
This works as far as I know with Grails 1.0.3 not sure of 1.0.4 and 1.1-betas but I assume they won't be decommissioning this feature in a while since it is important.
Never really got individual tests working though, as I have been unable to find anywhere that says how to run an individual test class.
Pointers to this will be appreciated.
In the coming days, I'll say something about mocking in Groovy using the 'as' feature.