Your doctor can diagnose acne based on the appearance of the skin. Testing is usually not required.
Habif TP. Acne, Rosacea, and Related Disorders. In: Clinical Dermatology. 4th ed.Mosby, Inc; 2004: 162-194.
Yan AC. Current concepts in acne management. Adolesc Med Clin. Oct 2006; 17(3): 613-37; abstract x-xi.