Embedded systems are nowadays already an essential part of our everyday life. Working in the background, several of them control important processes, such as the electric power delivery to each household. A failure of these systems may lead to big financial losses, in severe cases even to loss of innocent lives. Although built from two main components, hardware and software, the experience shows that the most reliability problems are caused by bugs in the implemented software. This fact makes the testing process of the embedded software a critical part of the system development process. By building hardware-in-the-loop simulations, the system testers have the possibility to examine the behavior of the developed system in an environment, which is very similar to the one present in the controlled plant, and able to automate the tests, so that regression testing can be done in shorter times.