This paper presents a method for automatically testing interactive multimodal systems. The method is based on the Lutess testing environment, originally dedicated to synchronous software specified using the Lustre language. The behaviour of synchronous systems, consisting of cycles starting by reading an external input and ending by issuing an output, is to a certain extent similar to the one of interactive systems. Under this hypothesis, the paper presents our method for automatically testing interactive multimodal systems using the Lutess environment. In particular, we show that automatic test data generation based on different strategies can be carried out. Furthermore, we show how multimodality-related properties can be specified in Lustre and integrated in test oracles.