re-bind a random number generator for testing

core.clj

(ns my-lib.core)

(def my-rand rand)

(defn my-fn []
  (take 3 (repeatedly my-rand)))

core_test.clj

(ns my-lib.core-test
  (:require [clojure.test :refer :all]
            [my-lib.core as core]))

; i'd like to re-bind the my-rand function here to make testing easier, but this doesn't work
(def core/my-rand (constantly 1))

(deftest my-fn
  (is (= (core/my-fn) '(1 1 1))))