Verifying that a save was called in a Service Test

I'm using Grails 2.4 and I have a helper service that creates a specific domain class, sets up the dependencies surrounding it and then finally saves the object to the database, within a promise.

How would I test this service?

An example of the service is:

def persist(name, objectId, depTwoId) {
  Person p = Person.findByName(name)
  Object o = Object.findById(objectId)

  RepObject rob = RepObject(p, o) //Ok you get the idea here

  def task = Promises.task { 
     rob.save()
  } 
}

I don't care, within the context of the unit test, if there was a save to the database. I just want to know that it was called.