[Common Lisp] Improve Concept Exercise: key-comparison

[verdammelt]

This issue describes how to improve the lillys-lasagna-leftover concept exercise for the Common Lisp track.

Getting started

Please please please read the docs before starting. Posting PRs without reading these docs will be a lot more frustrating for you during the review cycle, and exhaust Exercism's maintainers' time. So, before creating the issue, please read up on the following documents:

• The features of v3.
• Rationale for v3.
• What are concept exercise and how they are structured?

Please also watch the following video:

• The Anatomy of a Concept Exercise.

Goal

The tests for this exercise do not have any descriptions for the tests. The second argument to fiveam:test can be a destription string. This should be added to these tests so they can be useful to the student.

Help

If you have any questions while improving the exercise, please post the questions as comments in this issue.