Joint analysis unit test

[bfhealy]

Feature Summary
Having a unit test for the joint analysis code will help determine whether the code is working as intended, independent of issues with specific computing setups.

Alternative Solutions
It could be useful to run this test locally, even if it does not immediately work on GH Actions.

Implementation details
Setting up the configuration for this test could be difficult, especially for the GW data.

@tsunhopang, I'd be grateful for your thoughts on how best to implement this test.