Test framework?

[Tabasco]

The less practical, but possibly more effective approach is to start a server and then attempt some content or feature of great ambition.
Players will notify you of every quirk and quibble and from there you can do direct debugging.

This is a joke, of course. I offer nothing of value but the quiet chuckle that may keep you from weeping in the face of this beautiful but occasionally broken behemoth of a codebase.