Summary

test_ros2cli_daemon fails in the Rci__nightly-zenoh_ubuntu_noble_amd64 CI because the ROS 2 CLI daemon and the test node cannot discover each other — no isolated network is set up for the test, so cross-process node discovery fails.

Key Changes

• Add an autouse session-scoped fixture rmw_isolation that calls rmw_test_isolation_start() / rmw_test_isolation_stop() around the entire test session, before spawn_daemon() is called
• Import is wrapped in try/except ImportError so the fixture is a no-op on non-Zenoh RMW implementations where the package is absent
• Add rmw_test_fixture_implementation as a test dependency in package.xml

Breaking Changes

None

Deep Dive

rmw_test_isolation_start() starts an in-process Zenoh router on a random port and sets ZENOH_CONFIG_OVERRIDE=connect/endpoints=[tcp/127.0.0.1:<port>] in the current process environment (line 136–139). Any subprocess that inherits os.environ will have rmw_zenoh_cpp connect to that router and share the same discovery graph.

spawn_daemon() calls subprocess.Popen() with no explicit env=, so the daemon naturally inherits os.environ. Starting isolation before spawn_daemon() is therefore sufficient — the daemon picks up the router endpoint from the environment and connects to the same network as the test node.

Closes ros2/rmw_zenoh#932