input: Write a function to implement a web scraper in Python that extracts the top ten trending YouTube videos. The function should make a request to get the page content, parse the page content using BeautifulSoup, extract the list of trending videos, and then print the titles of the top ten trending videos. If the trending videos cannot be found or if there are fewer than ten trending videos, the function should print an appropriate message.
  
  assert extract_trending_videos()=='title1\ntitle2\ntitle3\ntitle4\ntitle5\ntitle6\ntitle7\ntitle8\ntitle9\ntitle10'
  assert extract_trending_videos()=='No trending videos found'
  
output: def extract_trending_videos():
      import requests
      from bs4 import BeautifulSoup
      
      url = "https://www.youtube.com/feed/trending"
      response = requests.get(url)
      soup = BeautifulSoup(response.content, 'html.parser')
      
      video_titles = []
      for title in soup.find_all('a', {'class': 'yt-simple-endpoint style-scope ytd-video-renderer'}):
          video_titles.append(title.text.strip())
      
      if len(video_titles) < 10:
          return 'No trending videos found'
      
      return '\n'.join(video_titles[:10])