A few minor grammatical and style nits in the prose added at the end of the diff:
> +The test module defines a base class with the tests methods that access the
> +``heapq`` module through a ``self.heapq`` class attribute, and two subclasses
> +that set this attribute to either the Python and C versions of the module.
I think that should be "Python or C version" (and -> or; versions -> version).
> +Note that only the two subclasses inherit from ``unittest.TestCase`` -- this
> +prevents the ``ExampleTest`` class to be detected as a ``TestCase`` subclass
"to be" should be "from being", I believe.
> +by ``unittest`` test discovery.
> +A ``skipUnless`` decorator can be added to the class that tests the C code
This should either have another newline inbetween or be reflowed. Either one paragraph or two makes sense to me, but I can't tell which way you actually meant it to go which makes for confusing reading of the ReST source.
As far as the example code changes, those look good to me :)