Uses simple-check to test that sorting is idempotent.

sort-idempotent.clj

(require '[simple-check.core :as sc])
(require '[simple-check.generators :as gen])
(require '[simple-check.properties :as prop])

(def sort-idempotent-prop
  (prop/for-all [v (gen/vector gen/int)]
    (= (sort v) (sort (sort v)))))

(sc/quick-check 100 sort-idempotent-prop)
;; => {:result true, :num-tests 100, :seed 1382488326530}