mikestreety, 
Managed to get Gitlab running PHP unit tests.
All the examples get you to copy a bash file and install dependencies in each run (e.g. https://docs.gitlab.com/ee/ci/examples/php.html#test-php-projects-using-the-docker-executor) so I made a Docker image with them pre-built.
Took job down from 45 seconds to ~3 seconds.
The docker images are open source:
https://github.com/liquidlight/docker-php-testing
(Yes the docs need updating...)
