private void EncryptDecryptFile(string fn)
        {
            var text          = _filesystem.LoadText(fn);
            var encryptedText = ROT13.EncryptDecrypt(text);

            _filesystem.ReplaceOriginalWithProcessed(fn, encryptedText);
            this.OnFileProcessed(fn);
        }
        public void Encrypt(string text, string expected)
        {
            var result = ROT13.EncryptDecrypt(text);

            Assert.Equal(expected, result);
        }