Hey Juju folks,
My colleague, Matúš Košút (@matuskosut), has developed a very handy tool called Jujuna for automating, testing and validating upgrades of OpenStack charms deployments. It allows us to quickly and systematically test both charm and actual OpenStack upgrades whenever there are new releases or changes made to our bundles. If you want to give it a spin with a small test deployment, then check out the examples from the docs.
Here is a short blog post introducing Jujuna with more details: https://huntdatacenter.github.io/jujuna/introduction/update/2018/11/23/introduction-to-jujuna.html