'L{failure.Failure}s need not be constructed with traceback objects. If
a C{Failure} has no traceback information at all, C{getTracebackObject}
just returns None.
None is a good value, because traceback.extract_tb(None) -> [].'

def test_getTracebackObjectWithoutTraceback(self):

    f = failure.Failure(Exception('some    error'))
    self.assertIsNone(f.getTracebackObject())
