input: Write a function to extract all email addresses from a given string using a regular expression. The function should return a list of all found email addresses. If no email addresses are found, the function should 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 here")==[]
  assert find_emails("")==[]
  assert find_emails("Single email: test@example.com")==["test@example.com"]
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