input: Write a function to implement a command-line interface for downloading subtitles for movies and TV shows. The function should accept one or more release paths as arguments, and optionally, specify the language and subtitle site to use. The function should support the following commands: "download", "exist", "test", "list", "help", and "version". If the "download" command is used, the function should attempt to download subtitles for each specified release path using the specified subtitle engine(s) and language. If the "exist" command is used, the function should check if subtitles for the specified release paths exist using the specified subtitle engine(s) and language. If the "test" command is used, the function should test the specified subtitle engines. If the "list" command is used, the function should list all available subtitle engines. If the "help" command or any list or version options are used, the function should provide appropriate help information or version details.
  
  
  assert download_subtitles(["/path/to/movie1", "/path/to/movie2"], ["opensubtitles"], "en")==None
  assert is_subtitles_exist(["/path/to/movie1", "/path/to/movie2"], ["opensubtitles"], "en")==None
  assert test_engines([])==None
  assert test_engines(["opensubtitles"])==None
  assert main() with arguments: ['--list'] outputs a list of available subtitle engines
  assert main() with arguments: ['--version'] outputs the version of the script
  assert main() with arguments: ['--help'] outputs help information
  
output: def main(args):
      if "--list" in args:
          # Code to list available subtitle engines
          pass
      elif "--version" in args:
          # Code to output the version of the script
          pass
      elif "--help" in args:
          # Code to output help information
          pass
      elif "download" in args:
          release_paths = args[args.index("download") + 1]
          engines = args[args.index("download") + 2]
          language = args[args.index("download") + 3]
          download_subtitles(release_paths, engines, language)
      elif "exist" in args:
          release_paths = args[args.index("exist") + 1]
          engines = args[args.index("exist") + 2]
          language = args[args.index("exist") + 3]
          is_subtitles_exist(release_paths, engines, language)
      elif "test" in args:
          engines = args[args.index("test") + 1]
          test_engines(engines)
      else:
          # Default action or error handling
          pass
  
  def download_subtitles(release_paths, engines, language):
      # Code to download subtitles
      pass
  
  def is_subtitles_exist(release_paths, engines, language):
      # Code to check if subtitles exist
      pass
  
  def test_engines(engines):
      # Code to test subtitle engines
      pass