Add test for utils

[aloctavodia]

We need to add tests for utils like process_group_variables_coords.

[PiyushPanwarFST]

Hi @aloctavodia,

I would like to work on this issue. I have looked into utils.py and agree that several functions are missing tests.

My plan is to start by adding tests for process_group_variables_coords as you suggested, and then I can progressively add tests for the other untested utility functions in the same PR.

If that approach sounds good, could you please assign this to me?

Thanks