input: Write a python function to scrape headlines from CNN's homepage using BeautifulSoup.
  assert isinstance(scrap_cnn(), list)
  assert len(scrap_cnn()) > 0
  assert all(isinstance(headline, str) for headline in scrap_cnn())
output: def scrap_cnn():
      import requests
      from bs4 import BeautifulSoup
  
      url = 'https://www.cnn.com'
      response = requests.get(url)
      soup = BeautifulSoup(response.content, 'html.parser')
  
      headlines = []
      for item in soup.find_all('h3'):
          if item.a:
              headlines.append(item.a.get_text())
          else:
              headlines.append(item.get_text())
  
      return headlines