input: Write a function to extract all public email addresses from a given string using regular expressions. The function should return a list of email addresses found in the string.
  
  import re
  
  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("No emails here.")==[]
  assert extract_emails("Contact me at info@website.org or support@site.io")==["info@website.org", "support@site.io"]
  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