Skeleton code files for exercises

IMO a really good piece of feedback:

There's quite a bit of boilerplate code required to complete the course's exercises. This boilerplate is not strictly relevant to the point of many exercises, and may distract from the important message.

We could add minimal skeleton files for each exercise, in which all of the irrelevant boilerplate code is prepared in advance.

No files or tests are named in the issue. Start by inventorying the course exercises and the boilerplate each currently requires, then define the minimal skeleton for each exercise; done means every exercise has a prepared file containing only the irrelevant setup needed to focus on its testing lesson.

Written by the indexing model from the issue text.