    # File lib/chef/cookbook/cookbook_collection.rb, line 36
        def initialize(cookbook_versions={})
          super() do |hash, key|
            raise Chef::Exceptions::CookbookNotFound, "Cookbook #{key} not found. " <<
              "If you're loading #{key} from another cookbook, make sure you configure the dependency in your metadata"
          end
          cookbook_versions.each{ |cookbook_name, cookbook_version| self[cookbook_name] = cookbook_version }
        end