How do I check my brake booster?

From RPRWiki

1. With the engine off, press the brake pedal several times. Then press it hard and hold that pressure for 15 seconds. If the pedal sinks, a brake line, wheel cylinder or master cylinder is faulty.

2. Start the engine with the pedal pressed. If the pedal sinks slightly, the booster is working. if the pedal height doesn't vary, the booster or check valve is faulty.

3. Press the brake pedal with the engine running. Then stop the engine. If the pedal height does not vary for 30 seconds the booster is OK. If the pedal rises, the booster is faulty.

4. With the engine off press the pedal several times with normal pressure. When the pedal is first pressed, it should be low. On consecutive applications, pedal height should gradually rise. If pedal height does not vary, check booster check valve. The check valve is the thing in the big vacuum line going to the booster, which is below the master cylinder in the engine compartment info thanks to rpr!