There is a common rule of thumb which dictates that you to stay two car lengths behind the next vehicle while driving so that you can stay in control of braking when the need arises. However, nothing beats the certainty of knowing exactly how your car would respond when you hit the brakes, how well the tires would grip the pavement, and at what exact point the ABS would kick in. Ultimately, it is satisfying knowing you can accelerate to high speeds and then slam on the brakes without causing any problems.
The methods used to test vehicle brakes have come a long way. There was even a time at which they used measuring tape to gauge stopping time. Nowadays, most people are familiar with the much more advanced and reliable pavement-reading laser systems. If you want pinpoint accuracy you could always opt for something involving GPS and accelerometers, but it may end up costing you quite a bit. In any event, the measuring-wheel-and-start-line combo is usually plenty for the budget-conscious car owner.
The braking characteristics of any vehicle is prone to changes as time goes on as a result of factors like tire traction, heating characteristics, brake fade, etc. The best tests give you a good measure of how the brakes perform under both dry and wet conditions. This lets you know how well the ABS is performing.
Brake testing is not just about stopping distance and stopping time. If you see your brake system leaning towards one and away from the other, there is bound to be something that needs fixing. You may see that the driver requires corrective steering every now and then, or that the back end swings out occasionally. Neither of those events is acceptable if you want your car to perform well and keep its travelers safe.
You would also need to watch the nosedive. Other than that, there is simply the ability to gauge how the brake system feels– do you get the responsive feel of an impending halt, or does it seem a slight gamble each time? Ideally, the brakes and pedal engage at the exact moment you put your foot down, and give ample feedback as to what should be expected. This way the driver reacts suitably and can avoid a crash.