I changed asserts with more specific assert methods.
e.g.: from assertTrue(sth == None) to assertIsNone(*) or
assertTrue(isinstance(inst, type)) to assertIsInstace(inst, type) or
assertTrue(not sth) to assertFalse(sth).
The code gets more readable, and a better description will be shown on fail.
Change-Id: Icdbf3c63fe8dd6db1129023885655a9f7032d4a7