Considering the test-suite tests the code from src paired with tests,
not the working directory (or even worse the overall include_path runtime
setting) should lead to relative path resolution, but just the relative
location to the path of the test itself.
Fix by making use of the __DIR__ constant to anchor the relative location
turning it into an absolute path.
Previously when checking out the repository and installing the source
package via `$ composer install` composer did spill deprecation notices for
four files not complying with the PSR-4 auto-loading standard.
This is a minor issue, composer install works and can be addressed by
fixing name-spaces (all of those three are in tests).
For the one function test, fixing the directory structure / dirname of the
(single) affected function test (fourth file).
