This is a joint article by me and Peter Kurhajec.

Unit testing is the practice of writing a test for a required functionality. In the world of “classical” IT software development, the concept of unit testing has been around for almost two decades. What is a standard procedure in languages such as Java, C++, .NET/C#, Python, etc. — has been completely lacking in the world of PLCs. The world of automation did not have the proper tools, and nor did it develop any comprehensive automated testing frameworks. Here we present two possible approaches for unit testing in Beckhoff’s TwinCAT 3.

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Dear TwinCAT/PLC developers,

I’m very happy to announce the release of the TcUnit-Runner, an open-source tool for integration of TwinCAT unit tests into a CI/CD toolchain automation server such as Jenkins. When TcUnit, the TwinCAT unit testing framework, was released back in December of 2018 I would never have imagined how widespread it would get. Since then, I’ve received e-mails from PLC developers every week with questions, improvement suggestions or just gratitude for this open-source software. The TcUnit framework has found its way into the full range of projects ranging from small machines to multi-billion € projects. With this response, I would say that there definitely is a need for unit testing in the world of automation. The adoption of TcUnit into TwinCAT projects across the globe has motivated the further development of TcUnit. One limitation of the TcUnit framework was that it was only possible to run the unit tests locally on your development machine (or PLC), and thus needed to be run manually every time a change in the software was made. Modern software practices advocate that software development should adhere to the practices of continuous integration/continuous delivery (CI/CD), so that tests would be run automatically when committing changes to version control. Thus, TcUnit-Runner was developed.

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