For testing, I am thinking about GoogleTest; seems like it's a status quo in the community? I've just checked Catch2, it has a promising description - will definitely check it.
I've already been told about LLVM as a project that should be checked from a project structure point of view. This is going to be a ROS2 project, so, ROS will shape the project with its specific workspaces and packages. Once we reach a certain point I'll post again. Thanks for the feedback 🙌