What is a test case?
Or, "The developers keep asking me to make a test case for a bug, but I don't know what that is."
A test case is an RPG file or plotscript that exhibits a known bug, and is designed to demonstrate it, often for testing purposes. Ideally, it has no material other than what is needed to trigger the bug. In other words, it's the lowest common denominator for triggering a bug.
Exhibits the Bug
This is important. A test case is useless if it doesn't exhibit the bug for which you're making the test case in the first place!
Contains no extra material
Generally, it doesn't even have to have graphics, other than (perhaps) a squiggle to represent an NPC. If plotscripting is needed to trigger a bug, there should only the script or scripts that directly trigger it.
If you can't seem to make a new file that has the bug, make a copy of the RPG, make a new map in the RPG, and work your way from there.
If you can't even do that, and you must use a full game, please include a save file that's as close as possible to the bug. It's not that we're lazy or anything, nor do we not want to play your game, but we just want to fix bugs.