input: Write a python function to extract email addresses from a given text using regular expressions.
  assert extract_emails("John Doe john@example.com, Jane Doe jane@example.com, Kevin Smith kevin@example.com") == ['john@example.com', 'jane@example.com', 'kevin@example.com']
  assert extract_emails("Contact us at support@service.com or sales@service.com") == ['support@service.com', 'sales@service.com']
  assert extract_emails("No emails here!") == []
output: def extract_emails(text):
      import re
      pattern = r'[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}'
      return re.findall(pattern, text)