UnitTests: fix mock assertions usage

Some unit tests used mock.Mock().assert_called_once() assertion.

This is wrong as the mock.Mock object has no such interface method,
so due to mock nature such wrong assertion do essentially nothing
and always pass.

Change-Id: I9ed5ba26aa099c362644a4f09d67a2f9bf36f382
Closes-Bug: #1336766
Merge "UnitTests: fix mock assertions usage"