This last example for the section covers the topic of encoding and decoding messages. It introduces the subject of how to pack information, or data, efficiently. Symbolic data allows the use of words, letters, or really anything to be the target of the code.
The testing in this section isn’t all that detailed. Several of the problems are concerned with just encoding and decoding the message properly, which is in itself a means of determining that the program is working correctly. That isn’t the only thing to consider, of course. If a message requires excessive amounts of processing power to encode or decode, it might not be worth it to transcode it. This is indeed considered in other exercises. While testing could be used to compare real-world results, they are probably better approached as thought problems.