An optical test system for use in testing fiber optical transmission systems and components comprises a modular construction in a single housing. The modular construction includes a plurality of laser source channels, a MUX, additional optical conditioning devices both upstream and downstream of the MUX, and a master controller for operating the system components in synchrony. The integral housing, together with the modular construction, provides increased structural density that occupies in many instances at least seventy percent less space than is required for other optical test systems. The use of a master controller to drive the system affords expanded system functionality.