An image sensor with an array of pixels is provided. In order to determine failure of transient signal generation circuitry within the image sensor, monitoring circuitry may be used to capture and adjust transient signals as the signals are being transmitted. The transient signals may be voltage booster signals that are generated by booster circuitry to adjust row control signal levels to be below the ground reference voltage or above the supply reference voltage before providing them to the array of image sensor pixels. The captured and adjusted transient signals may be multiplexed and transmitted through a common buffer circuit. The method of shifting/adjusting the captured voltages may also apply to static signals. The multiplexed adjusted signals may be converted from digital signals to analog signals with digital-to-analog conversion circuitry. The digitized signals may be transmitted to host circuitry for processing which may include pass/fail testing.