How-to doing CMake tests

[memsharded]

The docs explain cmake.test(), but it is missing what the CMakeLists.txt should look like, it might be useful an example or how-to, maybe with some testing framework as Catch as build_require

[danimtb]

At the bottom of this section there is an example on how to activate that: https://docs.conan.io/en/latest/howtos/header_only.html

It it would be even a nice topic to write in a blogpost using catch and following the recommendations for unit testing