The 'process-or-enqueue-command' function in pe-ext/services.clj has a branch which calls durable-enqueue-command if proccess-command throws. This branch is never hit during our unit tests, and that's fairly bad.
Testing this is a big pain. It should be easier once we get the new integration-test-in-clojure work committed, as we'll have a decent way to start / restart PDBs without clearing the database.