Use resource files in unit tests

[amasson42]

When writing a unit test, we should be able to load files that are in a resource folder in the repository.

name proposal : unit_tests_root

Unit tests should be executed with this folder as working directory so the main bundle ./ is from this folder and every test files are located starting from this folder.

This unit_tests_root folder should be ignored when packaging an application.

TODO: explain in a unit test, how to access this folder