Home Fitness Testing Guide
An initial fitness testing session can be used to give you an idea where your fitness levels are at the start of a training program, so that future testing can be compared to this and any changes can be noted.
Once a baseline level of fitness has been measured, regular testing can be used to monitor changes over time. A baseline is especially important if you are about to embark on a new training phase.
Fitness testing is also a useful form of motivation. The incentive to improve can often be provided by the 'goal' of a certain test score or rating.
More details are in the Home Fitness Test Manual
see also the articles about What to Test and How to Test.