Create tests for `load_model/metric/data`.

[c-salomonsen]

If anyone is up for the task, I think it makes sense to have tests for these functions as well.

[Seilmast]

I have some time atm. I'll start with load_model

[Seilmast]

Also finished making a test function for load_data.
I can have a look at making one for load_metric once issue #64 is solved so we know how the class will function.

[c-salomonsen]

@Seilmast Nice!, I'll add that I have barely started on this task as well. Please see #49, but currently there's only a test for load_data, and it ended up failing gh-actions tests, for some reason (I haven't really investigated this thoroughly).