# File lib/chef/provider/group.rb, line 61
      def define_resource_requirements
        requirements.assert(:modify) do |a| 
          a.assertion { @group_exists } 
          a.failure_message(Chef::Exceptions::Group, "Cannot modify #{@new_resource} - group does not exist!")
          a.whyrun("Group #{@new_resource} does not exist. Unless it would have been created earlier in this run, this attempt to modify it would fail.")
        end
      end