input: Write a function to extract all public email addresses from a given string using regular expressions. If the input string is empty, return an empty list. The function should return a list of all email addresses found in the input string.
  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("")==[]
  assert extract_emails("My email is john@example.com and jane@gmail.com")==["john@example.com", "jane@gmail.com"]
  assert extract_emails("admin@domain.com, support@domain.com")==["admin@domain.com", "support@domain.com"]
output: import re
  
  def extract_emails(text):
      if not text:
          return []
      pattern = r'\b[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Z|a-z]{2,}\b'
      return re.findall(pattern, text)