1. A test device for testing an electronic control system the test device having an addressable memory, and being connected to the control system; the test device being configured to run an environment model that is described by an environmental model variable having a value that can be stored at a particular address in the addressable memory and to execute a test model, the test device being configured such that the environment model can output environment model data to the control system and receive control system data from the control system; and, using the environment model, the test device simulates the functional environment of the control system to be tested; and the test model being configured to influence the environment model or the electronic control system or both the environmental model and control system, the test device further comprising an allocating unit, in which allocation of at least one environment model variable to at least one allocated address of the memory is filed such that the test model can effect the reading of the allocation unit to determine the memory address where the environment model variable value is stored and access that memory address during execution of the test model; and wherein the test model is configured to change the value of the environment model variable that is stored in the allocated memory address; and wherein values of a plurality of environment model variables can be modified, during one cycle of the environment model.