add a test which uses the create_subscription with queue size api

[wjwwood]

Connects to ros2/design#56.

[dirk-thomas]

Does this test have to replicate the whole testing with spin etc. or is it sufficient to only check the signature to create a subscription with a queue size?

[wjwwood]

Well, I figure it was worth making sure a subscription created with this API would result in a functioning subscription, but I can slim the test down further if you don't think that's important.

[dirk-thomas]

Related to my other comment (ros2/rclcpp#128 (comment)) I would think testing the functionality of the core functionality is enough. For the syntactic sugar API a simple test checking that a specific signature works would be enough.

[wjwwood]

Ok I simplified the test to just creating a subscription. The tests passed locally, so I won't run another CI.

[esteve]

+1

[dirk-thomas]

lgtm