Ref£º http://docs.openstack.org/developer/hacking/#real-world-import-order-examples
[H203] Use assertIs(Not)None to check for None (off by default) Unit test assertions
tend to give better messages for more specific assertions. As a result,
assertIsNone(...) is preferred over assertEqual(None, ...) and assertIs(None, ...),
and assertIsNotNone(...) is preferred over assertNotEqual(None, ...)
and assertIsNot(None, ...).
Change-Id: Idcf78fce02b01c41816a34efcb1264d69ce71706