Hey, thanks for the warm welcome.
Yes, I asked if there are any testing guidelines. But since the whole company is somehow in a restructuring process, there weren't defined yet. Maybe in the future but this would be far away.
To your proposal of 'contrived data': I just thought about the same approach. Just create some input data and see if we get the expected result. But I asked myself if there are some 'libraries' that I can already use. So I don't have to create it by myself.
Maybe there are also some libraries (e.g. some includes) that help me to build independing test cases. In principle just as JUnit is for Java.
But I'm satisfied with your answer.