Water leak from neighbors causing mold?

I live in an old apartment and my upstairs neighbor's water pipe was leaking, causing our hallway cupboard to become completely moldy. They refused to fix it for over a year and now say they fixed it three months ago. How do I know if they really have? There never was any drip and it seems to me that the mold is getting worse. But might it just get worse on its own, even if the pipe is fixed? We need to tear out the cupboard and rebuild and I of course don't want to do it until I'm sure the problem is solved.