fixes bug 1047569
The unit tests were calling a nonexistent assert_called() on the
mocks. This patch fixes the problem by using the correct assert for
checking that the mocked method was invoked.
Note: This patch does not fix the error in test_call_driver() because a
separate bug fix revises the test.
Change-Id: Ie62e2e64f314f9ba34761e63cd5d0d6e44c5d094
4633b61444