Tests need to be updated

Most of the unit tests are not up to date since the datamodules for each dataset are still being worked on.

In order to be able to run pytest while the datamodules are being refactored, failing tests have been marked with @pytest.mark.skip(reason="Test need to be updated"). All tests marked thus should either be updated or removed if the functionality is not used anymore.

Most of the cli tests should be working but have been marked due to #32 (closed).

Additionally, new tests have to be added for the new ConcatDataModule and CachingDataModule classes.

added Needs refactoring label

This has been fixed on !6 (merged).

closed