An optical integrated circuit is used to simultaneously test both the transmit fiber and the receive fiber in a fiber optic pair which extends between a telephone central office and a subscriber's site. By testing both fibers simultaneously testing time is cut in half without the loss of any important information, as fibers are replaced in pairs. In addition, the cost of test equipment is reduced considerably, as the expensive portions of the test equipment can be used for twice as many optical circuits as was heretofore possible. Finally, there are half as many connections needed between the optical switch and the optical integrated circuits built in accordance with the present invention, thereby simplifying their interconnections, and eliminating the extra cost in optical ports and interconnecting fiber.