input: Write a function to extract all email addresses from a given string. The function should use regular expressions to identify and return a list of all email addresses found in the input string. 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("multiple emails: abc@example.com, def@example.com, ghi@example.com")==["abc@example.com", "def@example.com", "ghi@example.com"]
  assert find_emails("check out these domains: abc@example.com, jkl@sub.example.com, mno@example.co.uk")==["abc@example.com", "jkl@sub.example.com", "mno@example.co.uk"]
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