You can clone with
HTTPS or Subversion.
I've just released http://pypi.python.org/pypi/fabtest/ package. It was extracted from a test suite for a project (https://bitbucket.org/kmike/django-fab-deploy/) similar to woven. I think fabtest can be useful for woven too.
Tests for Fabric commands can be written as standard unittests and each test can be run against clean (or prepared) VirtualBox VM snapshot using this package. It can run fab commands from python (very basic support) and manage VM snapshots much like django is handling DB rollbacks during tests.
Sounds good. I internally struggle between using an actual vm and using fabric's test ssh server to mock connections. The actual vm is practically a lot simpler but the ssh server is conceptually better.