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Empty-world simulation provides no useful /scan evidence, limiting sensor-oracle coverage #101
Description
Robot Model
Turtlebot4 Standard
ROS distro
Jazzy
Networking Configuration
Simple Discovery
OS
Ubuntu 24.04
Built from source or installed?
Installed
Package version
ros-jazzy-turtlebot4-simulator: 2.0.2-1noble.20260616.091643
ros-jazzy-turtlebot4-gz-bringup: 2.0.2-1noble.20260616.085653
ros-jazzy-turtlebot4-gz-toolbox: 2.0.2-1noble.20260615.145933
ros-jazzy-ros-gz: 1.0.22-1noble.20260616.074726
Gazebo: Harmonic / gz
Expected behaviour
For TurtleBot4 simulation tests that declare `/scan` as a watched topic, either:
1. useful `sensor_msgs/msg/LaserScan` samples should be recorded, or
2. the launch/test profile should explicitly mark scan coverage as disabled/unavailable for empty-world runs.
This would distinguish motion-control campaigns, where scan may be irrelevant, from sensor/hazard campaigns, where scan evidence is required.Actual behaviour
In empty/minimal-world headless campaigns, the motion-control findings were valid, but `/scan` did not provide useful evidence for sensor or obstacle-related checks.
The previous 1000-round report observed:
```text
All 941 saved error rosbags were parseable and had complete /odom plus /wheel_vels observations.
/scan was absent in all error rosbags because the campaign used the empty world;
this is not a motion-control bug signal.The latest report similarly concluded:
Empty-world scan false positive: not applicable to the reported acceleration bugs.
Scan absence or no returns are not the triggering oracle class here.
So this is not a motion-control bug. It is an observability/test-profile issue: empty-world simulation can make /scan unavailable or uninformative while users may still assume scan-based behavior is being exercised.
### Error messages
```bash
No terminal crash. Observed analysis result:
/scan was absent in empty-world error rosbags; scan was not the triggering oracle class.
To Reproduce
1. Start TurtleBot4 Standard simulation in an empty/minimal world.
2. Record `/scan`, `/odom`, `/cmd_vel`, and `/clock`.
3. Run a short motion command sequence or motion-control fuzz run.
4. Inspect the rosbag for `/scan` samples and useful finite scan ranges.
5. Observe that motion-control topics are present, while `/scan` may be absent or not useful for scan/hazard checks.Other notes
This should probably be handled as documentation/profile behavior rather than a controller bug. A useful improvement would be to document two explicit modes:
1. motion-control mode: empty/minimal world, `/scan` optional or marked unavailable
2. sensor/hazard mode: obstacle world, `/scan` required with useful finite ranges
Activity