input: Write a function to extract all email addresses from a given string. Return a list of all email addresses found in the string. If no email addresses are found, return an empty list. If the given string is empty, return an empty list.
  import re
  
  def find_emails(text):
      regex = r"([a-zA-Z0-9_.+-]+@[a-zA-Z0-9-]+\.[a-zA-Z0-9-.]+)"
      emails = re.findall(regex, text)
      return emails
  
  assert find_emails("This is an example with two emails: john@example.com, and jane@example.com")==["john@example.com", "jane@example.com"]
  assert find_emails("This string has no email addresses.")==[]
  assert find_emails("")==[]
output: import re
  
  def find_emails(text):
      regex = r"([a-zA-Z0-9_.+-]+@[a-zA-Z0-9-]+\.[a-zA-Z0-9-.]+)"
      emails = re.findall(regex, text)
      return emails