"Simulated time" used in the unit tests is too hard to understand

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I've spent a fair amount of time twice today debugging issues with the 
simulated time as implemented by asyncio.test_util.TestLoop, trying to modify 
the generator passed in to the constructor to deal with a different sequence of 
events. I've heard from others about this too.

I still can't even explain how it works -- I just gave up and copied-and-pasted 
some code from another test that had the desired effect.

Can we please replace the current machinery with something more understandable?

Original issue reported on code.google.com by gvanrossum@gmail.com on 9 Feb 2014 at 4:29