Added general method unit tests

[aburrell]

Description

Partially addresses #3 by adding unit tests for many of the general methods and simple file loading.

Type of change

Please delete options that are not relevant.

• New feature (non-breaking change which adds functionality or documentation)
• This change requires a documentation update

How Has This Been Tested?

Running the new unit tests

Test Configuration

• Operating system: OS X Mojave
• Version number: Python 3.9
• Any details about your local setup that are relevant: requires pysat develop branch.

Checklist:

• [x] Make sure you are merging into the develop (not main) branch
• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [x] I have linted the files updated in this pull request
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] New and existing unit tests pass locally with my changes
• [x] Any dependent changes have been merged and published in downstream modules
• [x] Add a note to CHANGELOG.md, summarizing the changes

If this is a release PR, replace the first item of the above checklist with the release checklist on the pysat wiki: https://github.com/pysat/pysat/wiki/Checklist-for-Release

[jklenzing]

I should have caught that prep_dir was used elsewhere in the pysat pull. Should have been deprecated there instead of just moved, which is why these tests are breaking. We can either use this with the develop branch of pysat, or switch back to the old path here and add a pass-through with DeprecationWarning in pysat develop to maintain usage.

[aburrell]

It doesn't look like that's why it's failing, though. It looks like it's failing because the tests aren't being skipped like they should be.

[aburrell]

@jklenzing it's passing now!