A CMOS image sensor including: an array of M×N pixels, the pixels of a same column being connected to a same output track, each pixel including a photodiode, a sense node, a transfer transistor, a reset transistor, and a read circuit; and a test circuit including an assembly of N elementary reference cells respectively connected to the N output tracks of the sensor, each cell including a resistor, a sense node, a transfer transistor, a reset transistor, and a read circuit, the N resistors being series-connected between first and second nodes of application of a reference voltage.