A design of optical testing device or system for fiber arrays is disclosed. According to one aspect of the invention, an array of light sources and an array of detectors are disclosed. One of the light sources is controlled to be turned on to test a designated fiber in an array of fibers being tested for connection issues. A microcontroller is configured to determine which one of the detectors is detecting a light beam from one of the light sources, and mark a channel of the array of fibers accordingly depending on if the one of the detectors is supposed to detect the light beam; if another one of the detectors detects the light beam; or if none of the detectors detects the light beam.