Structural Concolic Testing for Sequential Function Chart

Abstract

Graphical programming languages allow for well structured software and support comprehensibility and maintainability of the code. As for industrial applications, Sequential Function Chart(SFC) is a popular graphical language and was introduced by the IEC-61131-3 standard. Although providing powerful structuring elements that programmers can use to write better software, those elements are largely dropped when translating the software to a representation required for the application of formal methods. Even in widely used development-tools like CODESYS, SFCs are internally translated to the textual language Structured Text, coming from the same standard. This approach preserves the semantics needed for simulation, but can introduce significant overhead that impedes the application of formal methods, e.g. Concolic Testing, which is the focus of this work. To this end, we propose a novel Concolic Testing approach that utilises the structure of SFC in order to overcome the obstacles that keep traditional techniques from achieving high test-coverage in a reasonable amount of time. We compare our results to two approaches that work on a textual representation of the program.