Macro allowing for substitution of functions with predefined values.
Taken from "Clojure in action" page 180
Example:
(defn calc-x [x1 x2]
(* x1 x2))
(defn calc-y [y1 y2]
(/ y2 y1))
(defn some-client []
(println (calc-x 2 3) (calc-y 3 4)))
(stubbing [calc-x 1
calc-y 2
(some-client))

prints: "1 2" instead of "6 4/3"