The invention is concerned with an electronic device for testing and controlling the clearing action of an electronic yarn clearer. The device comprises an individual fault measuring circuitry connected to the yarn sensing head of the yarn clearer for detecting yarn faults such as thick and thin places, and selector means for separating the non-tolerable faults from the rest. By comparing the output of the device and the output of the yarn clearer, the non-tolerable faults which have not been cut-out by the yarn clearer are detected. It is possible to eliminate also the latter faults from the yarn by actuating the severing device of the clearer.