It seems that it is a known issue that codecov is not updated from Appveyor (which explains why we have pathetic coverage for the tzwin module and anything windows-related). See codecov/support#402. There seems to be some solution available, but the latest version of codecov-python does not have the fix.

Looks like in twisted/twisted#831 they pin to codecov == 2.0.5, though in the codecov issue a codecov-exe is mentioned. Shouldn't be terribly difficult to get it fixed, and that should give us a better idea of what needs to be done to get to 100% coverage.