From the https://clojure.org/guides/spec:
> Note that the :ret and :fn specs are not checked with instrumentation as validating the implementation should occur at testing time.
How can one enable :fn and :ret validation during tests, without using stest/check?
Perhaps https://stackoverflow.com/questions/40697841/howto-include-clojure-specd-functions-in-a-test-suite ?
I use the Orchestra library to instrument :ret (alongside the default :args): https://github.com/jeaye/orchestra