Sync tox with codecov requirements

[ajratner]

Is your feature request related to a problem? Please describe.

tox passes locally- including running coverage- but then codecov fails and blocks the PR.

Describe the solution you'd like

It's debatable how high the bar for maintaining coverage should be, and to what degree this is counterproductive friction... but either way, it would be more efficient if tox just failed, so could fix locally, and then be assured PR codecov test would pass.

[imskr]

I would like to work on this issue.