Massive boost leak from something...

[SupaSonic15]

Hello everybody,
I got a P0299 code so i hooked up a leak pressure tester. I couldn't get any pressure because it is all leaking out something mouted down by the driver-side axle. Its a metal canister-like thing that has a vacuum hose going from the brake master cylinder down to it and a rubber vent hose coming off of it and going through the inner fender liner. There is an electrial connector on it too. Does anyone know what this is?
I can't testv any further because all the air pressure just blows out it.

 

[SupaSonic15]

I found out it is a power brake booster pump. I have the vacuum line disconnected while testing for leaks but I hear all the air escaping through this. How do I disable it so I can complete a boost leak test?