Does anyone know of any novel / interest ways of unit testing papyrus scripts? I suppose I could just create a quest that uses every function in the testee script... actually, is it possible to manually trigger an 'event' through papyrus code?

There are a number of ways to trigger an event. Probably the easiest way for you if its a quest script is have one of the stages call the function for you, maybe the startup stage for when the quest begins.

You can also send any event to a script via a script, set the script as a property, call it something like MyScript, then use MyScript.YourFunction().

You can even send normal events... MyScript.OnActivate(akActionRef).