refactor: Removes unittest, so pytest operates as expected

[DanielArndt]

Currently, we have a mashup of unittest and pytest.

Although the class inherits from unittest, we're using pytest to run the tests. This works fine in the basic cases, but doesn't work when you try to use any of the features of either framework. For example, neither pytest parameterize or unitttest subtests work.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• I have added tests that validate the behaviour of the software
• I validated that new and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules