More automated testing

Some testing currently exists: a few unit tests for small helper classes, as well as a few GUI / command line running tests. To extend the coverage, we should add at least one command line running test for every filter in open_iA. Potentially we can also test starting different tools (though this is depending on the [Common Project Files](https://github.com/3dct/open_iA/issues/46) feature).

Look at existing command line running tests in the codebase to understand the pattern. Identify all filters in open_iA (likely in a filters directory or module). For each filter, create a test that runs it via the command line with sample data. Check if there's a test framework already set up (e.g., Google Test). Ensure tests can be run automatically, possibly via CI. 'Done' means every filter has at least one command line test.

Vom Indexierungsmodell aus dem Issue-Text verfasst.