An easy and simple test to check for a bad brake booster at home is to get into your car or other vehicle and start the engine and while the engine is idling press your brake pedal down and hold the brake pedal down for 30 seconds.
The brake pedal should hold it's position and if not then the brake booster is likely bad or there's a leak in your vacuum lines or manifold.
Another symptom of a bad brake booster is the need to use more force on the brake pedal when applying the brakes to get your vehicle to stop.