input: Write a function to implement an encryption and decryption application in Python using the AES algorithm. The function should take a plaintext string as input and return the encrypted text. Additionally, it should take an encrypted text as input and return the decrypted plaintext. The AES cipher should use a fixed key and operate in ECB mode.
  assert encrypt(b'This is a test')==b',\xf9\xa1O7\xab\x8b[{\x05\xfaY\xd6\xecE)\xc1'
  assert decrypt(b',\xf9\xa1O7\xab\x8b[{\x05\xfaY\xd6\xecE)\xc1')==b'This is a test'
  assert encrypt(b'')==b''
  assert decrypt(b'')==b''
output: from Crypto.Cipher import AES
  import base64
  
  def encrypt(plaintext):
      key = b'Sixteen byte key'
      cipher = AES.new(key, AES.MODE_ECB)
      padded_plaintext = plaintext + b'\0' * (AES.block_size - len(plaintext) % AES.block_size)
      encrypted_text = cipher.encrypt(padded_plaintext)
      return encrypted_text
  
  def decrypt(encrypted_text):
      key = b'Sixteen byte key'
      cipher = AES.new(key, AES.MODE_ECB)
      decrypted_text = cipher.decrypt(encrypted_text)
      return decrypted_text.rstrip(b'\0')