To carry out an operating check, bring the 
Brake Pedal down several times with the engine off to show that the reserve pedal distance does not change, then with the engine on check if the pedal goes down slightly. For airtightness check, switch on the engine for 1 or 2min, then switched off the engine and depress the brake pedal gently few times, if the pedal pressure is less with each depression, it indicate that the hydraulic booster is airtight. Set the brake pedal while the engine is running and shutdown the engine while the brake pedal remains depressed; when the reserve has been held for at least 30seconds there will be no reduction in the reserve travel of the pedal and hence the booster proved airtight. If the power brake booster units are removed do not disassemble them for they are sensitive and always use real tools, instead, get new or rebuilt ones. Base your procedure with the 
Brake Master Cylinder's removal and some models may require the removal of the 
Brake Lines crossing across in front of the MC. Slowly unplug the vacuum hose on the brake booster and unscrewing the brake pedal return spring on the top of the brake pedal as well as the clip and clevis pin. Secondly, to do that, unbolt the four machine screws on the brake booster to the fire wall and then pull the booster out, towards the rear of the vehicle until the studs come off the holes. For installation, this should be done in the reverse of the mentioned removal process and make sure that the booster mounting nuts are tightened to the recommended torque. It could also be used after fitting the master cylinder and brake hoses where one has to set the brake pedal height and freeplay together with bleeding the system depending on the situation.