The main part in the testing of the software is in the generation of test cases suitable for software system testing. The quality of the test cases plays a major role in reducing the time of software system testing and subsequently reduces the cost. The test cases, in model design stages, are used to detect the faults before implementing it. This early detection offers more flexibility to correct the faults in early stages rather than latter ones. The best of these tests, that covers both static and dynamic software system model specifications, is one of the challenges in the software testing. The static and dynamic specifications could be represented efficiently by Unified Modelling Language (UML) class diagram and sequence diagram. The work in this book shows that High Level Petri Nets (HLPN) can represent both of them in one model. Using a proper model in the representation of the software specifications is essential to generate proper test cases.