bots: Add manual command to get bot output.

This eliminates the need to setup dev environment and to
create a bot, setup zuliprc file, subscribe the bot to the
stream in order to try out a bot.

Manual command get-bot-output gives the bots response content
directly.

zulip_bots/zulip_bots/zulip_bot_output.py

@@ -0,0 +1,96 @@
+#!/usr/bin/env python
+from __future__ import print_function
+from __future__ import absolute_import
+
+import argparse
+import sys
+import os
+from types import ModuleType
+from importlib import import_module
+from os.path import basename, splitext
+
+import six
+import mock
+from mock import MagicMock, patch
+
+from zulip_bots.lib import run_message_handler_for_bot, StateHandler
+from zulip_bots.provision import provision_bot
+from zulip_bots.run import import_module_from_source
+
+
+def parse_args():
+    usage = '''
+        zulip-bot-output <bot_name> --message "Send this message to the bot"
+        Example: zulip-bot-output xkcd --message "1"
+        This tool can be used for testing bots by sending simple messages
+        and capturing the response.
+        (Internally, this program loads bot-related code from the
+        library code and then feeds the message provided
+        in the command to the library code to handle.)
+        '''
+
+    parser = argparse.ArgumentParser(usage=usage)
+    parser.add_argument('name',
+                        action='store',
+                        nargs='?',
+                        default=None,
+                        help='the name of an existing bot to run')
+    parser.add_argument('--message',
+                        action='store',
+                        help='the message content to send to the bot')
+
+    parser.add_argument('--path-to-bot',
+                        action='store',
+                        help='path to the file with the bot handler class')
+
+    parser.add_argument('--force',
+                        action='store_true',
+                        help='Try running the bot even if dependencies install fails.')
+
+    parser.add_argument('--provision',
+                        action='store_true',
+                        help='Install dependencies for the bot.')
+
+    options = parser.parse_args()
+    if not options.name and not options.path_to_bot:
+        error_message = """
+You must either specify the name of an existing bot or
+specify a path to the file (--path-to-bot) that contains
+the bot handler class.
+"""
+        parser.error(error_message)
+
+    return options
+
+def main():
+    # type: () -> None
+    options = parse_args()
+    bot_name = options.name
+    if options.path_to_bot:
+        if options.provision:
+            bot_dir = os.path.dirname(os.path.abspath(options.path_to_bot))
+            provision_bot(bot_dir, options.force)
+        lib_module = import_module_from_source(options.path_to_bot, name=bot_name)
+    elif options.name:
+        if options.provision:
+            current_dir = os.path.dirname(os.path.abspath(__file__))
+            bots_parent_dir = os.path.join(current_dir, "bots")
+            bot_dir = os.path.join(bots_parent_dir, options.name)
+            provision_bot(bot_dir, options.force)
+        lib_module = import_module('zulip_bots.bots.{bot}.{bot}'.format(bot=bot_name))
+
+    message = {'content': options.message}
+    message_handler = lib_module.handler_class()
+
+    with patch('zulip_bots.lib.ExternalBotHandler') as mock_bot_handler:
+        mock_bot_handler.send_reply = MagicMock() 
+        message_handler.handle_message(
+            message=message,
+            bot_handler=mock_bot_handler,
+            state_handler=StateHandler()
+        )
+        print("On sending ", options.name, " bot the following message:\n\"", options.message, "\"")
+        print("\nThe bot gives the following output message:\n\"", list(mock_bot_handler.send_reply.call_args)[0][1], "\"")
+
+if __name__ == '__main__':
+    main()