Rework python launch test

[christophfroehlich]

Background

Motivated by the great talk of @emersonknapp at ROSCon, we should cleanup our launchfiles.
Until the videos are online, you can have a look at the livestream at 6:10 and https://github.com/emersonknapp/roscon2025_launch_snippets

In this repo, we only have this one:

ros2_control/controller_manager/test/test_ros2_control_node_launch.py

Lines 49 to 85 in a7e0b3a

	# Executes the given launch file and checks if all nodes can be started
	@pytest.mark.launch_test
	def generate_test_description():
	robot_controllers = os.path.join(
	get_package_prefix("controller_manager"), "test", "test_ros2_control_node.yaml"
	)
	control_node = launch_ros.actions.Node(
	package="controller_manager",
	executable="ros2_control_node",
	parameters=[robot_controllers],
	output="both",
	)
	# Get URDF, without involving xacro
	urdf = os.path.join(
	get_package_share_directory("ros2_control_test_assets"),
	"urdf",
	"test_hardware_components.urdf",
	)
	with open(urdf) as infp:
	robot_description_content = infp.read()
	robot_description = {"robot_description": robot_description_content}
	robot_state_pub_node = launch_ros.actions.Node(
	package="robot_state_publisher",
	executable="robot_state_publisher",
	output="both",
	parameters=[robot_description],
	)
	ctrl_spawner = generate_controllers_spawner_launch_description(
	[
	"ctrl_with_parameters_and_type",
	],
	controller_params_files=[robot_controllers],
	)
	return LaunchDescription([robot_state_pub_node, control_node, ctrl_spawner, ReadyToTest()])

As a first step, remove the unnecessary local variables and remove the usage of os by using correct launch substitutions (~6:20 in the stream)

Instructions

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[shrujanus]

I want to working on this issue!

[shrujanus]

Thanks for adding me to this issue! I’ve opened PR #2781.
In this update, I replaced os usage with PathSubstitution and removed unused variables.

This is the first step, the next step could be introducing declarative launch arguments to allow substituting the URDF model being launched.

Please let me know if you have any suggestions or feedback!

[shrujanus]

@christophfroehlich I've made a new PR to master (#2789) and closed the old one. This PR has all the latest changes and is ready for review

[christophfroehlich]

@shrujanus I found a note in the docstring, which could get an update as well:

ros2_control/controller_manager/controller_manager/launch_utils.py

Line 40 in fc77935

controller_params_files=[os.path.join(get_package_share_directory('my_pkg'),

Could you include this in your PR please?