I should really understand how colcon works. Not should, HAVE TO.
How are you going to contribute to code at NVIDIA if you don’t even know how colcon works.
A good exercise for this is building ROS2 from source, and actually seeing what is happening under the hood. Brian Chen did this https://chenbrian.ca/posts/ros2_m1/#8-patch-python_cmake_module on his M1 Mac, so you should learn from him.
Learned from ashwin at NVIDIA.
colcon test --packages-select PACKAGE_NAME
Then, if there is an error, you can do
colcon test-result --verbose