[BUGFIX] Tests: Improve Mocking in ext:extbase

Change-Id: I61f7f92da42d691b0556f1e53b20d39eb082c12f
Resolves: #56700
Related: #51436
Releases: 6.2
Reviewed-on: https://review.typo3.org/28207
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn