Tests: 9 failed

[Hellseher]

This is a follow up issue to https://github.com/NASA-Planetary-Science/sbpy/issues/397.

I've managed to make tests running by providing --ignore=sbpy/spectroscopy/tests/test_specgrad.py option to pytests . Now I've got tests started but eventually failed with following trace (2023 LoC): sbpy-398-20240709204851.txt