Yes, the use case is for the fake driver. You are right in the sense that it might not belong in `nova::compute::libvirt`.

The problem originally came from puppetlabs-openstack which was always using `nova::compute::libvirt` in `openstack::all` and `openstack::compute` irregardless of our final intentions. In that specific case, there is no way to override `compute_drive` in `nova.conf` for test purposes and had therefore to implement an other openstack module to better suit our needs.

I will discuss with my teammates regarding the use of the fake driver so I can come up with a better explanation on the use case. The fake driver might as well go in a new class named `nova::compute::fake`. However I don't know how this would fit in puppetlabs-openstack.