Add test of optional ACA limits

[taldcroft]

Description

This adds a unit test that verifiers the functionality in #384.

As a small out-of-scope change, move to matplotlib.pyplot.switch_backend to avoid the linting problem with imports after code.

Interface impacts

None.

Testing

Unit tests

• Mac

Independent check of unit tests by Jean

• Linux

Functional tests

No functional testing.

[taldcroft]

@jeanconn - please approve if you are good with this.

[jeanconn]

I eye-balled the new git and model fetching and manipulation but haven't had a chance to do review on this yet.

[taldcroft]

Ah OK, I misinterpreted the scope of "This seems fine". No problem.

[jeanconn]

OK, so real testing question -- this makes sense but would there be other advantages to using a fixture to do this instead? Or have you not used a fixture because you prefer to explicitly test that ACA._set_aca_limits gets back to the 3.48 values?

[taldcroft]

I wasn't exactly sure how to do this with a fixture and decided this was good enough.

[jeanconn]

Looks good. The business with manually running ACA._set_aca_limits() to override the proseco "cache" and lazy load for these attributes reminded me... should proseco also be using @chandra_models.chandra_models_cache to get the model?

[taldcroft]

should proseco also be using @chandra_models.chandra_models_cache to get the model?

Good point. I think something like this can work and be a good thing. Next PR... #386