[TASK] Re-enable previously skipped unit tests

Take the chance to also clean up the test class a bit.

Change-Id: Ib2835aa4dc4c170d327f56dfcde134cf5871867b
Resolves: #40956
Releases: 6.0
Reviewed-on: http://review.typo3.org/14618
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters
Reviewed-by: Helmut Hummel
Tested-by: Helmut Hummel