Extract testable code and add test. · BenediktBurger/pyleco-extras@794a419

The job was canceled because "macos-latest_3_9" failed.

/Users/runner/micromamba/envs/pyleco-extras/lib/python3.12/site-packages/_pytest/assertion/rewrite.py:670: DeprecationWarning: ast.Str is deprecated and will be removed in Python 3.14; use ast.Constant instead

and isinstance(item.value, ast.Str)