4Clojure problem 29: http://www.4clojure.com/problem/29

gistfile1.clj

(defn test29 
  "Write a function which takes a string and returns a new string
  containing only the capital letters."
  [f]
  [(= (f "HeLlO, WoRlD!") "HLOWRD")
   (empty? (f "nothing"))
   (= (f "$#A(*&987Zf") "AZ")])

(test29 identity)