What is the proper procedure for testing the brakes?

The proper procedure for testing the brakes involves pumping the brake pedal and checking for firmness after starting the vehicle. This process is essential because it allows the driver to ensure that the brake system is functioning correctly before moving. A firm brake pedal indicates that the brake system has pressure and is operational, which is vital for safe driving. If the brake pedal feels soft or spongy, it may suggest a problem such as air in the brake lines or a fluid leak, necessitating further inspection before driving.

The other options do not adequately assess the brake system's functionality in the same comprehensive manner. For instance, checking brakes while stationary might not reveal issues that only become apparent when the vehicle is in motion, and pressing the brakes while driving can potentially compromise safety if brake failure were to occur. Checking brake fluid levels is a good maintenance practice but does not directly assess the brakes' immediate readiness for use. Therefore, the method of pumping the brake pedal after starting the vehicle is the most effective approach for ensuring the vehicle's braking system is in proper working condition.