input: Write a function to extract all email addresses from a given string using regular expressions. Return a list of all found emails. If the input 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("No emails in this text.")==[]
  assert find_emails("Mixed formats like john.doe@example.com and jane+2022@example.us")==['john.doe@example.com', 'jane+2022@example.us']
  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