Investigate possility of creating code coverage for Scheme code

JavaScript code has ~86% code covered by unit tests. But there is no way to tell what is the code coverage on the Scheme code.

References:

* [How would you create test coverage tool?](https://www.reddit.com/r/ProgrammingLanguages/comments/mo1g0v/how_would_you_create_test_coverage_tool/)
* [Haskell Program Coverage](https://web.archive.org/web/20210410120834/http://www.ittc.ku.edu/~andygill/papers/Hpc07.pdf)
* [Approach to Scheme Code Test Coverage](https://www.reddit.com/r/scheme/comments/1alwhb8/approach_to_scheme_code_test_coverage/)

The issue names no repository files, tests, or entry points; start by examining how the existing JavaScript unit tests are run and where the Scheme implementation is measured. Compare the linked coverage approaches, and consider the work complete only when the project has a reproducible Scheme coverage method and a way to report its result.

Written by the indexing model from the issue text.