code: def ensure_directories_end_in_separator(opts_dict):
      
      assert_has_input_output(opts_dict)
      assert 'is_dir' in opts_dict
      if opts_dict['is_dir']:
          opts_dict['input'] = add_suffix(opts_dict['input'],
                                          get_path_separator())
      opts_dict['output'] = add_suffix(opts_dict['output'], get_path_separator())
docs: Adds a path separator to the end of the input and output directories,
      if they don't already have them.
  
      :param opts_dict: dictionary that will be modified