See data-apis/array-api#29.

We could compare numerical functions against an arbitrary precision library. The question is how off something should be for it to be a failure, but at least we can report the largest deviation (hypothesis makes this straightforward).

mpmath is a good option, as it is pure Python and well tested as it is used inside of SymPy.

One technical issue is that mpmath's arbitrary precision floats have infinite range, unlike machine floats which overflow and underflow. As far as I can remember, that is the main difference between an mpmath.mpf with dps=15 and a machine float, but there may be other differences as well that I'm not remembering.