This is my code:
import praw

bot = praw.Reddit(user_agent='bot',
                  client_id='',
                  client_secret='',
                  username='',
                  password='')

subreddit = bot.subreddit('test')

comments = subreddit.stream.comments()

for comment in comments:
    text = comment.body # Fetch body
    author = comment.author # Fetch author
    if 'wow this is a test' in text.lower():
        # Generate a message
        message = "yes".format(author)

        comment.reply(message) # Send message

This is the error i get:

Traceback (most recent call last):
  File "C:\Users\user\Desktop\redditbot\bot.py", line 13, in <module>
    for comment in comments:
  File "C:\Users\user\Desktop\python\lib\site-packages\praw\models\util.py", line 171, in stream_generator
    limit=limit, params={'before': before_attribute}))):
  File "C:\Users\user\Desktop\python\lib\site-packages\praw\models\listing\generator.py", line 52, in __next__
    self._next_batch()
  File "C:\Users\user\Desktop\python\lib\site-packages\praw\models\listing\generator.py", line 62, in _next_batch
    self._listing = self._reddit.get(self.url, params=self.params)
  File "C:\Users\user\Desktop\python\lib\site-packages\praw\reddit.py", line 408, in get
    data = self.request('GET', path, params=params)
  File "C:\Users\user\Desktop\python\lib\site-packages\praw\reddit.py", line 534, in request
    params=params)
  File "C:\Users\user\Desktop\python\lib\site-packages\prawcore\sessions.py", line 185, in request
    params=params, url=url)
  File "C:\Users\user\Desktop\python\lib\site-packages\prawcore\sessions.py", line 116, in _request_with_retries
    data, files, json, method, params, retries, url)
  File "C:\Users\user\Desktop\python\lib\site-packages\prawcore\sessions.py", line 101, in _make_request
    params=params)
  File "C:\Users\user\Desktop\python\lib\site-packages\prawcore\rate_limit.py", line 35, in call
    kwargs['headers'] = set_header_callback()
  File "C:\Users\user\Desktop\python\lib\site-packages\prawcore\sessions.py", line 145, in _set_header_callback
    self._authorizer.refresh()
  File "C:\Users\user\Desktop\python\lib\site-packages\prawcore\auth.py", line 328, in refresh
    password=self._password)
  File "C:\Users\user\Desktop\python\lib\site-packages\prawcore\auth.py", line 142, in _request_token
    payload.get('error_description'))
prawcore.exceptions.OAuthException: invalid_grant error processing request