This link was useful, but somewhat incomplete. I’m still looking for a good general reference for building a suite of unit tests to test an actual application, instead of just simple theoretical apps.
One thing I did discover – my tests were all failing, due to something seemingly completely out of my control – the unlock_mutex method, buried deep in the ActiveRecord base.
Some investigation revealed that this was likely related to the “use_transaction_fixtures” control variable. A bit of googling revealed that I could just turn it off, which fixed the problem. Interestingly, the documentation says that this is only required for MyISAM database structures. However, I verified that I use InnoDB. However, this “MyISAM-only” fix fixed the problem, so there we are.