An electronic device includes an internal device and a voltage tester. The internal device includes a power supply source input terminal. The voltage tester supplies one of first and second power supply source voltages to the power supply source input terminal of the internal device, in response to a test signal. The first and second power supply source voltages have different voltage levels. The first power supply source voltage has a voltage level within a normal range required for normal operations of the internal device. The second power supply source voltage has an abnormal voltage level outside the normal range.