input: Write a python function to extract and return news titles and their corresponding links from a given URL. 
  assert extract_news('http://www.example.com/latest-news') == [('Title1', 'http://www.example.com/link1'), ('Title2', 'http://www.example.com/link2')]
  assert extract_news('http://www.example.com/news') == [('News1', 'http://www.example.com/news1'), ('News2', 'http://www.example.com/news2')]
output: def extract_news(url):
      import requests
      from bs4 import BeautifulSoup
      
      response = requests.get(url)
      soup = BeautifulSoup(response.content, 'html.parser')
      
      news_items = []
      
      for item in soup.find_all('div', class_='news-item'):
          title = item.find('h2').text
          link = item.find('a')['href']
          news_items.append((title, link))
      
      return news_items