input: Write a python function to get the HTML source of a web page using the requests library.
  assert 'html' in get_html_source('https://www.example.com')
  assert '<title>Example Domain</title>' in get_html_source('https://www.example.com')
  assert 'Example Domain' in get_html_source('https://www.example.com')
output: def get_html_source(url):
      import requests
      response = requests.get(url)
      return response.text