Though I did not use this patch verbatim, thank you, Oliver, for the impetus to improve coverage. Now, coverage of the logging package is:

logging/__init__.py 99% (97%)
logging/config.py 89% (85%)
logging/handlers.py 65% (60%)

where the brackets include branch coverage measurements. Not too shabby, so I'll close this issue now: I think future coverage increases will need to focus on the handlers.