Streamline the test coverage process when a new plugin is added

As part of #3225695: Support entity types whose entity bundle type does not end with `_type` and entities without created date → to add a taxonomy_term entity to the test structure there are several hard-coded places where the new entity has to be added. If these are not done, it gives the impression that full test coverage of the new entity is working because all tests pass. The process can be improved so the addition only has to be done in one place and therefore and test failures will immediately show up.