Get content of topic from launch_testing_ros::WaitForTopics

[LastStarDust]

Feature request

Feature description

In the WaitForTopics sample code here, I see how I can easily test that a node has published a topic with a certain name, but it is not shown how to test the actual content of the topic.

It would be very helpful if the content of the topic could be available to the tester, too.

Implementation considerations

Looking deeper at the source code here, it seems that only the topic name is stored.

Because of Python duck-typing it should be more or less easy to just return the content of the topic. Something like

    def callback_template(self, topic_name):

        def topic_callback(data):
            if topic_name not in self.received_topics:
                self.get_logger().debug('Message received for ' + topic_name)
                self.received_topics.add(topic_name)
                self.received_messages[topic_name].append(data)
            if self.received_topics == self.expected_topics:
                self.msg_event_object.set()

        return topic_callback

where self.received_messages is a dictionary where the key is the topic name and the value is the list of received messages. Just as an example.

[LastStarDust]

If you deem this feature useful, I would be available to implement it and make a pull request.

[adityapande-1995]

Hi @LastStarDust ! That is a good suggestion. While WaitForTopics was originally meant to just block until all the mentioned topics receive messages, it can be useful to know what the message was. A couple of questions :

1. Should the message stored be the last message before WaitForTopics() returns, or the first message a topic receives ?
2. Should this workflow be preferred over adding a separate subscriber ?

If you could open a PR, I'll be happy to review it.

[LastStarDust]

@adityapande-1995 Hello. Thank you for your feedback. I created a pull request #353 for this feature as you suggested.

[Ryanf55]

Hello, I would like to re-iterate how important this feature is for creating production-ready ROS code that is tested at the middleware level.

In following the V-model of development in commercial projects that use ROS 2, it is very important to have tooling to send and receive messages, services, and actions to validate that the behavior of a node is in line with the requirements, and to be able to have reliable automated tests that can prove adherence to the requirements.

Asserting that the node published a message, but ignoring the content is not sufficient enough of a test to demonstrate adherence to design requirements for any asynchronous publishers.

A great example is to check that the header timestamp is not zero and is the same as the event that triggered the publish. If a node receives an event, and a developer incorrectly uses the wrong timestamping by calling node->now(), that is a big problem for time-critical behaviors, and it's super common in development to mess up the timestamping. Take a look at my recent NAV2 work on TwistStamped support as proof these pitfalls occur in some of the "best" FOSS ROS 2 code.

Currently, my team is maintaining a layer on top of launch_ros to perform this kind of testing, and would much prefer to work with the ROS community to improve test infrastructure. Being able to have a batteries-included test infrastructure will help companies focus on testing their node behaviors rather than writing boilerplate or infra.

LastStarDust has put a great amount of work to supporting this kind of testing, however his work hasn't gotten to humble where it can be used in production. I ask the maintainers and OSRC to focus some renewed time and energy on contributions that support the production testing of ROS 2.

[Ryanf55]

This is now backported to all active distros. It is now solved. Please close the issue as completed.

[clalancette]

Closing as solved by #353