Stubbing a function using clojure spec

spec-stub-function.clj

;;;;;;;;;;; STUBBING A FUNCTION

(defn select-id [id]
  ; real code would connect to db, just simulating here
  {:col1 (rand-int 101)
   :col2 (rand-nth ["Joe" "Bob" "Bill" "Sally"])})

(s/def ::col1 nat-int?)
(s/def ::col2 (s/with-gen string? #(gen/such-that (complement empty?) (gen/string-alphanumeric))))
(s/def ::db-row (s/keys :req-un [::col1 ::col2]))

(s/fdef select-id
        :args (s/cat :id pos-int?)
        :ret ::db-row)

;(select-id 5)
;=> {:col1 37, :col2 "Bill"}

; now turn on instrumenting -- function not called, only gen'd
(stest/instrument `select-id {:stub #{`select-id}})
;(select-id 5)
;=> {:col1 347, :col2 "1rfT3Pw"}