Include unit tests in refactoring work

[jtlangevin]

The unit tests for ecm_prep and run are in some cases a bit bloated and could use some trimming down and reorganization for clarity.

[jtlangevin]

A few suggestions from @rHorsey in PR #564:

I don't think it's worth it priority wise but I really think the tests could be improved by breaking out the dictionary data into json and leaving just the test code in the files. Again - to far down the list of important things to matter but ya. I'm approving this, but @jtlangevin could you point me to an example BSS BPS ECM? I'm curious / unclear what that would look like from the test. lgtm

Not now, but in the future we should start doing some indications of allowable values within lists and dicts in docstrings.