I don't get that behavior

This works fine for example. Even though if you run:

(sgen/generate (s/gen `add))

when an instrumented fdef with an fspec is checked, the :args spec of the fspec is generated and then the fspec function is invoked to verify it conforms to its spec

many people find this surprising and I expect we will ultimately change it

what do you think of my suggestion above as a temporary measure (to not call validate-fn when *fspec-iterations* is 0 or nil)?

also, I appreciate that you are considering options for this 🙂

Oh I see, you mean if you spec a higher order function on an fdef. Interesting, I don't think I ever specced one before.