In ros2cli, there are tests that command line tools produce expected output. e.g. https://github.com/ros2/ros2cli/blob/96cf5b949d1aa870111bba0664eca1c359d3307c/ros2lifecycle/test/test_cli.py#L363-L374

notably this command which uses expect_output:

        assert launch_testing.tools.expect_output(
            expected_lines=['unconfigured [1]'],
            text=lifecycle_command.output,
            strict=True
        )

When these tests fail, they are reported in CI with an extremely generic error message, stating only the test case and its arguments (if parameterized). Also the error message shows up again, under the heading "stack trace"

https://ci.ros2.org/view/nightly/job/nightly_osx_debug/1588/testReport/ros2lifecycle.src.ros2.ros2cli.ros2lifecycle.test/test_cli/test_cli/

Error Message

some test cases have failed: test_cli[rmw_cyclonedds_cpp] failed at TestROS2LifecycleCLI.test_list_all_lifecycle_hidden_node_transitions_with_hidden_flag[rmw_cyclonedds_...
test_cli[rmw_cyclonedds_cpp] failed at TestROS2LifecycleCLI.test_list_all_lifecycle_node_transitions[rmw_cyclonedds_cpp]

Stacktrace

some test cases have failed:
test_cli[rmw_cyclonedds_cpp] failed at TestROS2LifecycleCLI.test_list_all_lifecycle_hidden_node_transitions_with_hidden_flag[rmw_cyclonedds_cpp]
...
test_cli[rmw_cyclonedds_cpp] failed at TestROS2LifecycleCLI.test_list_all_lifecycle_node_transitions[rmw_cyclonedds_cpp]