Jupsen is a juju plugin that includes a number of sub commands that are used to cause problems in juju networks. You can see it in action here https://www.youtube.com/watch?v=xp54gcMMUfQ
As an example you can create a partition between a wordpress and mysql unit by running part:
juju jupsen part wordpress/0 mysql/0
You can fix this partition by running
juju jupsen heal wordpress/0 mysql/0
go install github.com/mattyw/jupsen/juju-jupsen/...
juju jupsen help