Python Caesar Cipher

CaesarCipher.py

#!/usr/bin/python
# Filename: CaesarCipher.py
# Author: Hercules Lemke Merscher

class CaesarCipher(object):
    ''' Cifra de Cesar.'''

    def encrypt(self, msg, key):
        if msg == None: return None

        size = len(msg)
        encrypted_msg = []

        for i in range(size):
            character = ord(msg[i])
            encrypted_msg.append(chr(character + key))

        encrypted_msg = ''.join(encrypted_msg)
        return encrypted_msg

    def decrypt(self, encrypted_msg, key):
        return self.encrypt(encrypted_msg, -key)

CaesarCipherTest.py

#!/usr/bin/python
# Filename: CaesarCipherTest.py
# Author: Hercules Lemke Merscher

import unittest
from CaesarCipher import *

class CaesarCipherTest(unittest.TestCase):
    ''' Testes da classe CaesarCipher.'''

    cipher = CaesarCipher()

    # testes para o metodo "encrypt"
    def testEncryptWithNullString(self):
        self.assertEqual(None, self.cipher.encrypt(None, 3))

    def testEncryptWithEmptyString(self):
        self.assertEqual("", self.cipher.encrypt("", 3))

    def testEncryptWithKeyEqualZero(self):
        self.assertEqual("abc", self.cipher.encrypt("abc", 0))

    def testEncryptWithKeyEqualOne(self):
        self.assertEqual("bcd", self.cipher.encrypt("abc", 1))

    def testEncryptWithKeyEqualThree(self):
        self.assertEqual("def", self.cipher.encrypt("abc", 3))

    def testEncryptMyNameWithKeyEqualSix(self):
        self.assertEqual("Nkxi{rky", self.cipher.encrypt("Hercules", 6))

    # testes para o metodo "decrypt"
    def testDecryptWithNullString(self):
        self.assertEqual(None, self.cipher.decrypt(None, 3))

    def testDecryptWithEmptyString(self):
        self.assertEqual("", self.cipher.decrypt("", 3))

    def testDecryptWithKeyEqualZero(self):
        self.assertEqual("abc", self.cipher.decrypt("abc", 0))

    def testDecryptWithKeyEqualOne(self):
        self.assertEqual("abc", self.cipher.decrypt("bcd", 1))

    def testDecryptWithKeyEqualThree(self):
        self.assertEqual("abc", self.cipher.decrypt("def", 3))

    def testDecryptMyNameEncryptedWithKeyEqualSix(self):
        self.assertEqual("Hercules", self.cipher.decrypt("Nkxi{rky", 6))

# executando todos os testes
unittest.main()