input: Write a python function to encrypt a message using AES encryption in CBC mode.
  assert encrypt("My Secret Message", b'#1\x84\xdc\x06\x0c\x12\xe8\x0c\xd7 \x9d\x03\xd4*\xdd[\x85') == b"B\xf5{5<\xec~\xf9\xc9\x8f_3\x04\x95\x15'\x90\xd2\\\xfc\xd9\x03\xdc\x1dr\x1b"
  assert encrypt("Hello World", b'#1\x84\xdc\x06\x0c\x12\xe8\x0c\xd7 \x9d\x03\xd4*\xdd[\x85') != b"B\xf5{5<\xec~\xf9\xc9\x8f_3\x04\x95\x15'\x90\xd2\\\xfc\xd9\x03\xdc\x1dr\x1b"
  assert len(encrypt("A"*16, b'#1\x84\xdc\x06\x0c\x12\xe8\x0c\xd7 \x9d\x03\xd4*\xdd[\x85')) == 16
output: from Crypto.Cipher import AES
  from Crypto.Util.Padding import pad
  import os
  
  def encrypt(message, key):
      cipher = AES.new(key, AES.MODE_CBC)
      iv = cipher.iv
      ciphertext = cipher.encrypt(pad(message.encode(), AES.block_size))
      return iv + ciphertext