Enhance test cases

[JanSkn]

Is your feature request related to a problem? Please describe.
So far, test coverage is just at about 24% although all relevant functions have at least 1 test. Enhance tests to achieve a higher coverage.
Used Framework: Pytest

You can also use others.

Describe the solution you'd like
Test coverage of at least 70%.

Describe alternatives you've considered
/

Additional context