The "testing" I had in mind would be to investigate how inaccurate the algorithm is given some functional form.  For example, if one had some tabulated data that that thought was really f(x), how would trapz do on the integral?

If the namespace is already polluted with the other versions, is there any loss to including the functional ones? 

That said, I think the use case for this is tiny, so your point of discouraging use is fine.