Implement unit tests for pipeline element 'NumericalFilterProcessor'

[bossenti]

This issue is about implementing unit tests for our pipeline element NumericalFilterProcessor. An example of how to write unit tests for pipeline elements can be found here.

Mentoring

As this issue is marked as a good first issue and for the hacktoberfest event: one of @dominikriemer, @tenthe, @RobertIndie, or @bossenti are happy to provide help for getting started, just tag (one of) them if you want to start working on this issue and need some help.

[nncha96]

Hi, can I take this issue?

[dominikriemer]

Hi @nncha96 great :-)