input: Write a function to extract all public email addresses from a given string. Return a list of all the matching email addresses using regular expressions. If no email addresses are found, return an empty list. 
  
  assert extract_emails("My email is john@example.com and yours is john@gmail.com.")==['john@example.com', 'john@gmail.com']
  assert extract_emails("No emails in this string.")==[]
  assert extract_emails("")==[]
  assert extract_emails("Contact us at information@example.com or support@example.org")==['information@example.com', 'support@example.org']
  assert extract_emails("john.doe@example.com is a valid email address")==['john.doe@example.com']
output: import re
  
  def extract_emails(text):
      pattern = r'\b[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Z|a-z]{2,}\b'
      return re.findall(pattern, text)