Methods are disclosed for testing the functionality of a system element to be used inside a control and/or data processing system as well as, in essentially the opposite direction, for designing a system model having at least one transmission function for modeling a control and/or data transmission system with at least one system element. A data-processing device for performing this method is also disclosed, which device comprises a signal unit that can be coupled to a constructed system element for producing a control and/or data transmission system, for reading out, querying or receiving a signal output of the system element in response to a predetermined signal voltage applied at the system element, an evaluation unit for evaluating the signal output as a function of the input signal in order to analyze the system element, and a processing unit for associating the analyzed system element with a transmission function.