This is meant to be a simple container in which to run functional tests. It has JDK 1.7.0_60 installed, the necessary environment variables set, PhantomJS installed in the PATH, and git installed.
To use, run it with a -v flag, mounting a persistent directory from your Docker host in which to store your git repositories. Make sure that your private key is in that directory beforehand. Here is the command I used while running it in boot2docker:
docker run -i -v /var/lib/files/mountpoints/functional-testing:/persistent -t devis/functional-testing /bin/bash
Once inside, you still need to get set up for Git. There is be a script in /root which, when run, will copy a key "id_rsa" from your shared host directory and set up git with a name and email defined in the script. If you have already registered the private key with git, you should now be able to clone a Geb/Spock functional testing repository to /persistent and start running phantomjs tests!