@jbrockmendel Great tests, thanks for this. I have the one comment that you can take or not take about the parametrized fixture, and this also needs a changelog. I'm about to merge #890 so you may want to rebase if you're making the changes after that.

Rebased and edited with requested changes.

@pganssle gentle ping for this, #891, and #894 (and if were really ambitious, #883 and #737). I'm a dateutil-productivity hot-streak and want to get the most out of it before inevitably getting distracted.