Provide study test utilities

[mikix]

It might be nice to encourage unit tests in studies and provide some tooling for it.

In the hypertension study (and still-WIP data-metrics study), I've got a little test harness method that runs a study on some ndjson and compares the resulting tables against some csvs.

Super basic, but pretty useful. We could copy that into the Library, as a starting block.

[dogversioning]

Some discussion around this for posterity:

• don't perscribe a test framework other than what's in the standard lib - but hooks for test frameworks are fine, and should be set up in a reuseable way
• The method reference in the above comment is a good starting point for a generalized, holistic runner
• It may also be nice to provide a version of the mock_db/mock_db_config functions in the library as part of an importable testing module for more targeted/incremental testing

[mikix]

Matt and I just had a quick slack convo about this and I wanted to mention that we both are leaning away from exposing a way to create raw resource tables (like the Library testbed or the data-metrics harness do) and towards mocking/creating the core tables directly if we can.

Faster certainly, and also easier to mock edge cases directly.

Maybe its API looks similar to the testbed class (e.g. add_patient()), but it would just operate on the core tables instead of raw tables.