Dealing with simulation and modelling tasks with digital tools in mathematics lessons puts high demands on teachers when it comes to the preparation and implementation of lessons. These must be met in teacher education. To measure the pre-service mathematics teachers' professional knowledge for teaching simulations and mathematical modelling with digital tools, we propose a theory-based model and subsequently present items of an associated test instrument. Using a one-parameter Rasch model, we show that the underlying model can be confirmed empirically and discuss the potentials and limitations of the results.