POU-Oriented Unit Testing of IEC 61131-3 Control Software

Software testing is an important part of project development. Depending on system type and size, it is performed variously. Unit testing is one of the available approaches that is used to ensure that behavior of small software parts is consistent with requirements. It allows to improve software quality and decrease overall costs. Despite the fact that such an approach is commonly judged as a vital concept, it is not usual in control software. In this paper, the comprehensive approach to test the IEC 61131-3 software using unit tests is presented. It supports to create tests in two ways-either in textual and graphical IEC 61131-3 languages or in the CPTest+ dedicated test definition language. The latter is equipped with many advanced features, such as test fixtures and inclusions, parameterized and analog signal extensions, mock objects, as well as a few kinds of suites. The overall solution runs on the developer and testing station; hence, it does not have significant impact on performance of the control program and tests are more reliable and repeatable. To explain the concept, the simple running example is presented in this paper. The described solution has been introduced in the CPDev engineering environment for programming controllers.