new_contents: #!/usr/bin/env python3
  
  
  import string
  import unittest
  # modules I've written:
  from ..rot13 import rot13
  
  
  class Rot13TestCase(unittest.TestCase):
      """
      Test the rot13 function.
      
      It should convert any ASCII English letter chars in the given string to
      ROT13 and back.
      """
      
      def setUp(self):
          self.ascii_letters = string.ascii_letters
          self.ascii_letters_rot13 = string.ascii_lowercase[13:] + \
                                     string.ascii_lowercase[:13] + \
                                     string.ascii_uppercase[13:] + \
                                     string.ascii_uppercase[:13]
      
      def test_converts_to_rot13_correctly(self):
          self.assertEqual(self.ascii_letters_rot13, rot13(self.ascii_letters))
  
  
  def main():
      unittest.main()
  
  
  if __name__ == '__main__':
      main()
  
subject: Add tests for rot13