def explode_dirs
      exploded_files = []
      files.each do |file|
        if File.directory?(file)
          exploded_files << explode(file)
        else
          exploded_files << file
        end
      end
      @files = exploded_files.flatten
    end
def explode_dirs
      exploded_files = []
      files.each do |file|
        if File.directory?(file)
          exploded_files << explode(file)
        else
          exploded_files << file
        end
      end
      @files = exploded_files.flatten
    end
todo: unit test