    # File lib/chef/provider/package/dpkg.rb, line 33
            def define_resource_requirements
              super
              requirements.assert(:install) do |a|
                a.assertion{ not @new_resource.source.nil? }
                a.failure_message Chef::Exceptions::Package, "Source for package #{@new_resource.name} required for action install"
              end

              # TODO this was originally written for any action in which .source is provided
              # but would it make more sense to only look at source if the action is :install?
              requirements.assert(:all_actions) do |a|
                a.assertion { @source_exists }
                a.failure_message Chef::Exceptions::Package, "Package #{@new_resource.name} not found: #{@new_resource.source}"
                a.whyrun "Assuming it would have been previously downloaded."
              end
            end