# File lib/fog/aws/models/iam/group.rb, line 13
        def add_user(user_or_name)
          requires :name

          user = if user_or_name.is_a?(Fog::AWS::IAM::User)
                   user_or_name
                 else
                   service.users.new(:id => user_or_name)
                 end

          service.add_user_to_group(self.name, user.identity)
          merge_attributes(:users => self.users + [user])
        end