Clojure has a binding method that allows you to stub out a method. According to the (cdoc binding), one example is:

(defn mymax [x y]
  (min x y))

(defn find-max [x y]
  (max x y))

(binding [max mymax]
  (find-max 10 20))  ;; => 10

Unfortunately this doesn’t work anymore. When you run it, you’ll get this error:

user=> (binding [max mymax] (find-max 10 20))
IllegalStateException Can't dynamically bind non-dynamic var: clojure.core/max  clojure.lang.Var.pushThreadBindings (Var.java:353)

The only way to fix it is by defining the method as dynamic.

(defn ^:dynamic foo []
  (println "hello"))

I’m able to do this for my own code, but I haven’t figured out how to alter the meta data for an existing function, such as the max used in the example above.

Comment: you can do this for existing functions using with-redefs