Remove duplicate docstrings and refactor abstract test classes to use class variables

[Roel]

• I have read and followed the guidelines in the CONTRIBUTING document
• I have checked to ensure there aren't other open Pull Requests for the same update/change
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

This PR removes docstrings from subclasses when they are identical to the ones provided in the upper class.

It also refactors the abstract test classes to use class variables instead of getter functions.

Should fix #262