class_docstr: Test the Ubuntu Corpus trainer class.
class_docstr_tok: ["Test","the","Ubuntu","Corpus","trainer","class","."]
docstr: Test the case that the corpus file exists.
docstr_tok: ["Test","the","case","that","the","corpus","file","exists","."]
code: def test_download_file_exists(self):
      """
      Test the case that the corpus file exists.
      """
      import requests
  
      file_path = os.path.join(
          self.trainer.data_directory, "download.tgz"
      )
      open(file_path, "a").close()
  
      requests.get = Mock(side_effect=self._mock_get_response)
      download_url = "https://example.com/download.tgz"
      self.trainer.download(download_url, show_status=False)
  
      # Remove the dummy download_url
      os.remove(file_path)
  
      self.assertFalse(requests.get.called)
  
imports: from unittest.mock import Mock
  from io import BytesIO
  import tarfile
  import os
  from tests.base_case import ChatBotTestCase
  from chatterbot.trainers import UbuntuCorpusTrainer
label_desc: Use image node_id 9 for calling the UbuntuCorpusTrainerTestCase obj's underlying member method code with example usage: obj.test_download_file_exists() without return types