Add integration tests: Do the robots actually move?

[christophfroehlich]

We currently test only if the systems (hardware+controllers) are launched correctly.

But there is no test if the robots actually move. This leads to issues with configuration, like reported in #1086

We can use a similar pattern like in gz_ros2_control_tests and adapt them to the demos.

[github-actions]

This issue is being labeled as stale because it has been open 45 days with no activity. It will be automatically closed after another 45 days without follow-ups.

[kamal2730]

Hello @christophfroehlich, I would like to give this issue a try. Could you please assign it to me?

[kamal2730]

Hi @christophfroehlich, I'm planning to create a shared ros2_control_demo_test_utils package containing Python executables (such as test_forward_command) that send commands and validate joint state changes, exiting with code 0 on success.

Each example's launch test will run these as subprocesses via launch_testing.tools.launch_process and verify the exit code.

I'll start with example_1 and open a PR for feedback. Does this approach sound good?