#!/usr/bin/env python3

""" Caesar Cipher

A caesar cipher is a simple substitution cipher where each letter of the

plain text is substituted with a letter found by moving 'n' places down the

alphabet. For an example, if the input plain text is:

abcd xyz

and the shift value, n, is 4. The encrypted text would be:

efgh bcd

You are to write a function which accepts two arguments, a plain-text

message and a number of letters to shift in the cipher. The function will

return an encrypted string with all letters being transformed while all

punctuation and whitespace remains unchanged.

Note: You can assume the plain text is all lowercase ascii, except for

whitespace and punctuation.

"""

import unittest

def caesar(plain_text, shift_num=1):

# TODO: Your code goes here!

result = plain_text

return result

class CaesarTestCase(unittest.TestCase):

def test_a(self):

start = "aaa"

result = caesar(start, 1)

self.assertEqual(result, "bbb")

result = caesar(start, 5)

self.assertEqual(result, "fff")

def test_punctuation(self):

start = "aaa.bbb"

result = caesar(start, 1)

self.assertEqual(result, "bbb.ccc")

result = caesar(start, -1)

self.assertEqual(result, "zzz.aaa")

def test_whitespace(self):

start = "aaa bb b"

result = caesar(start, 1)

self.assertEqual(result, "bbb cc c")

result = caesar(start, 3)

self.assertEqual(result, "ddd ee e")

def test_wraparound(self):

start = "abc"

result = caesar(start, -1)

self.assertEqual(result, "zab")

result = caesar(start, -2)

self.assertEqual(result, "yza")

result = caesar(start, -3)

self.assertEqual(result, "xyz")

start = "xyz"

result = caesar(start, 1)

self.assertEqual(result, "yza")

result = caesar(start, 2)

self.assertEqual(result, "zab")

result = caesar(start, 3)

self.assertEqual(result, "abc")

if __name__ == "__main__":

unittest.main()