Is there a way to test it or should I just replace it?

Car runs better after new MAP sensor, but not perfect.

 

Put a fuel pressure gauge on it. Rev up the motor a little. If the gauge moves, then the regualtor works.

 

Pull the vacuum line off. If fuel comes out it's broken and should be replaced. Bad fuel pressure could also be a condition of a clogged fuel filter (easy to replace) or a bad fuel pump (not so easy to replace).

What problem are you having exactly?