input: Write a python function to extract all URLs from a given text using regular expressions.
  assert extract_urls("The websites I like to visit are https://www.google.com and https://www.facebook.com")==['https://www.google.com', 'https://www.facebook.com']
  assert extract_urls("Check out http://example.com and https://secure-site.org")==['http://example.com', 'https://secure-site.org']
  assert extract_urls("No URLs here!")==[]
output: def extract_urls(text):
      import re
      url_pattern = r'https?://\S+'
      return re.findall(url_pattern, text)