Hi @Vabs95-ttn
I just ran into this issue as well and created a PR to fix this by providing an implementation for the filtering: https://github.com/apache/sling-org-apache-sling-testing-osgi-mock/pull/7/files
Fyi: when an OSGi Mock Service is somehow not doing exactly what is needed / reflects a real world scenario, you can override it by specifying another implementation with a higher service.ranking, so you could have very well created your own implementation and hooked it in there.
In case of the MockConfigurationAdmin before the PR I just linked, it is not possible to override exception cases for the listConfigurations-method with Mockito, as it defines no exceptions to be thrown. You can however make a new interface implementation that delegates the method calls to the MockConfigurationAdmin, where you do specify that it throws all the exceptions.
That issue is also fixed in that PR.