youtube bot: Replace sys.exit() with bot_handler.quit().

zulip_bots/zulip_bots/bots/youtube/test_youtube.py

@@ -39,7 +39,7 @@ class TestYoutubeBot(BotTestCase):
 
         with self.mock_config_info({'key': 'somethinginvalid', 'number_of_results': '5', 'video_region': 'US'}), \
                 self.mock_http_conversation('test_invalid_key'), \
-                self.assertRaises(SystemExit) as se:  # type: ignore
+                self.assertRaises(bot_handler.BotQuitException):
                     bot.initialize(bot_handler)
 
     def test_multiple(self) -> None:

zulip_bots/zulip_bots/bots/youtube/youtube.py

@@ -31,9 +31,8 @@ class YoutubeHandler(object):
             search_youtube('test', self.config_info['key'], self.config_info['video_region'])
         except HTTPError as e:
             if (e.response.json()['error']['errors'][0]['reason'] == 'keyInvalid'):
-                logging.error('Invalid key.'
+                bot_handler.quit('Invalid key.'
                                  'Follow the instructions in doc.md for setting API key.')
-                sys.exit(1)
             else:
                 raise
         except ConnectionError: