input: Write a function to extract all public email addresses from a given string. The function should return a list of email addresses found in the input string. Use a regular expression that matches common email patterns. If no emails are found, the function should return an empty list.
  
  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("") == []
output: 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