Message 131151 - Python tracker

Benjamin, thanks for the pointers! The attached patch now uses assertIs() and assertIsNot(), and calls self.fail() instead of using the exception from "support".

In the future I would like some way to determine when test coverage is fully achieved, so that I do not come back to this module every few months and have to re-discover why it is not 100%. But for the moment I have indeed removed the pragmas, pending a better approach!