When hydraulic brakes are functioning properly, after pumping the brake pedal three times and then applying firm pressure, the expected behavior is for the pedal to remain steady and not move. This indicates that the brake system is holding pressure and that there are no leaks or air in the lines. A pedal that does not move suggests that the hydraulic system is sealed and effectively transmitting force from the brake pedal to the brake components, allowing the vehicle to stop efficiently.
If the brake pedal were to depress slightly, sink to the floor, or vibrate, it would indicate potential issues within the system. Slight depression could suggest worn brake components or air in the hydraulic lines, while sinking to the floor typically signifies a serious problem such as a fluid leak or failure in the brake master cylinder. Vibrating could also indicate a malfunction in the brake system, perhaps due to warped rotors or issues with the brake linings. Thus, the answer that the pedal should not move at all confirms that the brake system is in good working order.