input: Write a function to extract all public email addresses from a given string. Use regular expressions to match email formats and return a list of all found email addresses.
  
  def extract_emails(text):
    emails = re.findall(r"[a-zA-Z0-9_.+-]+@[a-zA-Z0-9-]+\.[a-zA-Z0-9-.]+", text)
    return emails
  
  assert extract_emails("My email is john@example.com and yours is john@gmail.com")==['john@example.com', 'john@gmail.com']
  assert extract_emails("Contact us at help@company.com or support@company.com")==['help@company.com', 'support@company.com']
  assert extract_emails("No emails here")==[]
  assert extract_emails("")==[]
output: def extract_emails(text):
    emails = re.findall(r"[a-zA-Z0-9_.+-]+@[a-zA-Z0-9-]+\.[a-zA-Z0-9-.]+", text)
    return emails