def check_files
      @found_files = []
      check_required_files
      check_optional_files
      # Add feed files of zip to the list of files to be processed
      @source.feed_definition.files.each do |req|
        @found_files << req if filenames.include?(req.filename)
      end
    end
def check_files
      @found_files = []
      check_required_files
      check_optional_files
      # Add feed files of zip to the list of files to be processed
      @source.feed_definition.files.each do |req|
        @found_files << req if filenames.include?(req.filename)
      end
    end
Parse the filenames in the feed and check which required and optional
 files are present.
 @raise [RequiredFilenamesMissing] if the feed is missing a file which is
  marked as "required" in the [FeedDefinition]