The present invention provides a method and apparatus for testing a valve control system in an aircraft fuel supply system having a plurality of control valves, wherein the control system includes a processor adapted to receive feedback signals from each of the plurality of control valves, the method comprising the steps of: connecting a test device to the control system such that the test device is connected for signal transmission to the processor; outputting a signal to the processor simulating a feedback signal from at least one of the control valves; detecting a control signal which is output by the processor to the at least one of the control valves; and identifying the detected control signal which is output by the processor to the control valve.