I could reproduce it successfully in various environments (docker images using the nightly archives, the dashing debs and building dashing from source), and the problem also appears on packages from the ros2.repos for this is not related to the code here.
For the last couple days CI has been broken on master due to pytest errors: https://travis-ci.org/Karsten1987/roscon2018/builds/540535685
I could reproduce it successfully in various environments (docker images using the nightly archives, the dashing debs and building dashing from source), and the problem also appears on packages from the ros2.repos for this is not related to the code here.
A workaround is available at https://github.com/mikaelarguedas/ros2ci/pull/18 and fixes CI for both nightly and dashing: https://travis-ci.org/Karsten1987/roscon2018/builds/541281526?utm_source=github_status&utm_medium=notification