Feature requests: isolated testings (with ROS_DOMAIN_ID)

[huweiATgithub]

Feature request

Feature description

The LaunchTestRunner or the LaunchROSTestItem should support running in an isolated environment like what ros2 test do: https://github.com/ros2/ros_testing/blob/a60a6d11b5761288f2238651ee4f48c3b99ad373/ros2test/ros2test/command/test.py#L39-L50
 

Implementation considerations

Suggested by the implementation in ros2test, we can write the runtest member function of the class LaunchROSTestItem as follows:

    def runtest(self):
        with contextlib.ExitStack() as stack:
            if "ROS_DOMAIN_ID" not in os.environ:
                domain_id = stack.enter_context(domain_coordinator.domain_id())
                os.environ["ROS_DOMAIN_ID"] = str(domain_id)
            if "ROS_DOMAIN_ID" in os.environ:
                print(f"ROS_DOMAIN_ID: {os.environ['ROS_DOMAIN_ID']}")
            return super().runtest()

To offer this feature as an option, we can supply arguments to the pytest mark

@pytest.mark.rostest(isolated=True)

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I can submit a pull request implementing this feature if the proposal is approved.

[cottsay]

I think this would be a great addition to launch_ros, and look forward to seeing a pull request implementing it.

Thanks!