test package is barely explained

So far, its explanation is fragmented in different pages and the main reference in getting started has no dedicated link. The https://docs.conan.io/en/latest/creating_packages/getting_started.html is the start point, but only comments about the folder, but no recipe example.

You can check yourself: https://docs.conan.io/en/latest/search.html?q=test+package&check_keywords=yes&area=default