[TASK] Unit tests for getFileAbsFileName

Change-Id: If2d8c342e6632ab86a7744ac6d019fcc1f7af74c
Resolves: #73572
Related: #73516
Releases: master
Reviewed-on: https://review.typo3.org/46783


Reviewed-by: Andreas Fernandez <typo3@scripting-base.de>
Tested-by: Andreas Fernandez <typo3@scripting-base.de>
Reviewed-by: Frank Naegler <frank.naegler@typo3.org>
Tested-by: Frank Naegler <frank.naegler@typo3.org>