FizzBuzz Kata in Clojure

fizzbuzz.clj

(ns fizzbuzz (:use clojure.test))

(defn fizzbuzz [n]
  (let [ret (str (when (= (rem n 3) 0) "Fizz") 
                 (when (= (rem n 5) 0) "Buzz"))]
    (if (empty? ret) n ret)))

(deftest fizzbuzz-test
  (is (= (fizzbuzz 1) 1))
  (is (= (fizzbuzz 2) 2))
  (is (= (fizzbuzz 3) "Fizz"))
  (is (= (fizzbuzz 4) 4))
  (is (= (fizzbuzz 5) "Buzz"))
  (is (= (fizzbuzz 15) "FizzBuzz"))
  )

(run-tests)