I'll answer my own question here. In my spec_helper.rb I've put the
following:
require 'rubigen'
require 'rubigen/helpers/generator_test_helper'
# Must set before requiring generator libs.
TMP_ROOT = File.join(File.dirname(__FILE__),"sandbox","generated")
PROJECT_NAME = 'example'
PROJECT_FOLDER = File.join(TMP_ROOT,PROJECT_NAME)
APP_ROOT = File.join(TMP_ROOT, PROJECT_NAME)
-Adam