Fitness testing involves evaluating a client's current physical abilities in order to identify areas for improvement, write an effective exercise program to help achieve their goals, and monitor their progress. It follows the PIPI structure - assessing the purpose, importance, procedure, and interpretation. The procedure involves static tests like measurements and skin folds followed by dynamic tests of muscular fitness, cardiorespiratory endurance, and flexibility. Principles dictate tests should be relevant, valid, reliable, and allow interpretation against norms and baselines.