[TASK] Add unit tests for mergeRecursiveWithOverrule

Resolves: #63817
Releases: master
Change-Id: I27d86eae5a59f0b6f5509dd247ac44415643d1b6
Reviewed-on: http://review.typo3.org/35365
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Stephan Großberndt <stephan@grossberndt.de>
Tested-by: Stephan Großberndt <stephan@grossberndt.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>