To run the docker example one has to have docker-ce installed and accessible via "unix:///var/run/docker.sock" (the default). The default docker bridge network also needs to be accessible from the pytest executor since the test tries to establish an ssh connection to the container (again the default after a standard installation of docker-ce).
After following steps similar to Getting started the demo can be run with:
pytest -s --lg-env env.yaml test_shell.py
Successfully tested against Docker version 18.06.1-ce, build e68fc7a. But it should work with later versions as well.