I tried using AsyncioDocTestRunner that inherits from DocTestRunner and most of the current DocTestRunner is synchronous and the execution happens in __run that seems to cause problem due to name mangling inheriting and changing it. Also python -m doctest by default uses testmod/testfile that use DocTestRunner so I thought to change DocTestRunner would be simpler and existing code can use added doctest flag without changing runner. 

To be little more clear by each line I meant each example. So in below "async with session.get(url) as resp:\n    text = await resp.text()" counts as a single example whose code object is evaluated in asyncio.run which I said as per line by mistake.

>>> async with session.get(url) as resp:
...     text = await resp.text()


Your concerns are reasonable about asyncio.run per example seem to be over kill and might not work in few cases. I also didn't think about trio. I will look into those. Thanks for the pointers.