A method and a device for testing a control unit, in which sensor data are transmitted over a network connection to a real or simulated control unit, which data are calculated by a data processing system using simulation, in which the simulation of the sensor data takes place at least in part with at least one graphics processor of at least one graphics processor unit of the data processing system. The simulated sensor data are encoded in image data that are output via a visualization interface to a data conversion unit that simulates a visualization unit connected to the visualization interface. Via the data conversion unit the received image data are converted into packet data containing the sensor data through the network connection to the control unit.