A testing system includes a computer (10), a motherboard (31) of a mobile phone, a photosensitive component (33) and a measuring device. The motherboard of the mobile phone is connected to the computer. The motherboard of the mobile phone includes a keyboard light (313) disposed thereon. The photosensitive component is capable of sensing the brightness of the keyboard light. The measuring device is connected to the photosensitive component. The measuring device is capable of measuring the resistance of the photosensitive component and transmitting the resistance to the computer. The computer is capable of comparing the resistance with a pre-determined range of values to determine whether the keyboard light of the motherboard meets a standard.