Test Case Generation Method For The Software Of Railway Signaling Interlocking System

Computer-based interlocking system is the key equipment that performing the route control to ensure the safety and improve the capacity for railway operation. The software of interlocking system is a kind of safety critical application.lt is vitally necessary to research the testing method of interlocking software,especially the method of the test case generation of the interlocking software.At present,the study of the interlocking software testing is still not complete,the reasons are as follows.On one hand,considering this kind of safety critical system,the testing process costs complex work and takes a long testing period,and the test cases are compiled by experts based on the interlocking table and requirements specification.In the compiling process,it will be unavoidably introducing some human factors which may cause a greatly harmful impact on the testing efficiency.On the other hand,for the complex logic of the interlocking system,it is easy to understand that the comprehension of the interlocking system may have some limitations and deviations,because of which the risk of errors may increase greatly.Therefore,a CPN(Colored Petri Nets)-based interlocking software test case generation method was proposed.First,it carried out the formalized description,analysis and verification for the interlocking system. And then an algorithm was implemented to generate test cases on the basis of ensuring the correctness of the software model.The main work is as follows:(1) Based on the summarization of the formal modeling and the test case generation method, the function structure of the interlocking system was described in detail,the state change of route control was analyzed mainly, and the test requirement of interlocking software was defined.(2) According to the properties of colored Petri nets and the modeling rules of CPN Tools,a kind of formal description could be concluded for the control logic of interlocking software.Firstly,the logic relation of interlocking system was abstracted, and the CPN model of each layer was built respectively according to the different levels of the structure. And then each layer of the CPN model was integrated.(3) The hierarchical CPN model of interlocking software was built by the example of the route establishing process.The place was used to represent device state,and the transition was used to indicate the change of device state. According to the condition of interlocking system, the HCPN model of route control process was established,and then the model was simulated and verified.From the state space report of the model,we can see that all of the states can be found in the model,which proved the correctness of the model.(4) It turned out to be state reachability diagram by calculating the state space of the model above,according to which all the starting and ending state nodes were found and redundant nodes were removed.Then a depth-first-search algorithm was implemented to find the inputs and outputs of test cases,which finally leaded to the generation of the test cases based on the CPN model.It is proved that the software can automatically generate test cases on the basis of the CPN models.and the test cases can cover all the places,transitions and arcs in the model.On the premise of completely matching the coverage specifications,we can reduce the repeatability of the test cases.