Add a simple example that shows how to leverage typescript in a test

[simskij]

When we simplified this project from the previous (significantly more complete example) we, unfortunately, ended up with only two test files.

This means the repo no longer contains any example on how to define your own types and have typescripts compile-time type-checking prevent you from using types in a non-compatible way. This should be re-added, but as this is a template repo, it needs to be small, useful, and non-invasive. 🤔