turtle uses it because that was the file that I made work when I was playing with 'make doctest'.  I think being able to use the testsetup directive would be good.  It could also them be used (I think!) to put resource directives in the docs that would control whether or not (eg) turtle was run via regertest '-u', making it not run by default.  What make doctest does is to write the doctests out to to a file and then run them with the normal doctest tools, so there ought to be a way to integrate with it.  I guess how easy that is depends on how easy it is to run sphinx on just one file...which might not be easy.