Automated test sequence generation for FBD programs

Abstract

Function Block Diagram (FBD) is one of the programming languages for programmable logic control-lers (PLCs). PLC programs are repeatedly run within a scan time for every execution. FBD programs consist of variables and function elements. Among the constituents of FBD programs, function blocks and feedback variables use the input or output values of the previous scan cycle to operate on. Because FBD programs are used for implementing safety-critical systems such as nuclear reactor protection systems, the ability to auto-matically generate of effective test cases is crucial. Researchers have recently developed automated test gen-eration techniques that satisfied structural test coverage criteria for FBD programs using symbolic execution, but the previous work was limited to generating test inputs for a single scan cycle

it could not generate test sequences for consecutive scan cycles. Such test sequences are essential for testing FBD programs that have internal states and feedback variables. This paper extends previous work by generating test sequences for FBD programs with internal states in a fully automated manner. The key technique involves gathering constraints for each consecutive scan cycle and solving those constraints using an SMT solver. We evaluate the effectiveness of the generated test set using mutation analysis with several subject programs, including real-world reactor protection system programs. The results of the empirical evaluation suggest that the proposed approach can generate effective test sequences for FBD programs.