It would be really handy to have a comment here explaining what the intent actually is
  -- something like the one in the "zero_div" methods, where it says "Ensure cube behaviour matches numpy operator"

I guess what we're really doing here is to compare the function result with the operator result. 
I'd put explanatory comments on the abstract  "op" and "func" definitions, too, as you can't see here what kind of thing they're intended to be set to.
This file is the place to explain what the point of it all is.