test_mocks.clj

;; Taken from https://github.com/Prismatic/eng-practices/blob/master/clojure/20130821-testing-principles.md

(defmacro test-double
  "Creates a test double of a function given a fully qualified function name.
   Behaves like a function, and then stores arguments values in a map, 
   with key as the argument name"
  ([] `(gensym))

  ([fqfn]                  ; fully qualified function for argument naming
     (let [args (first (:arglists (meta (resolve fqfn))))
           args-count (count args)]
       `(let [received-args# (repeatedly ~args-count #(atom nil))]
          (reify
            clojure.lang.IFn
            (invoke [this# ~@args]
              (doseq [[arg# received#] (map list ~args received-args#)]
                (reset! received# arg#)))

            clojure.lang.ILookup
            (valAt [this# k# not-found#]
              (-> (map (fn [arg# received#] [(keyword arg#) @received#]) '~args received-args#)
                  (#(into {} %))
                  (get k# not-found#)))

            (valAt [this# k#] (.valAt this# k# nil)))))))

(test/deftest record-public-linkage-event-test
  (let [mongo-datastore (test-double)
        env :test
        request {:cookies {"stage_p_public" {:value "foobar-cookie"}}}
        user-id (rand-int 10)
        event-body {:type "public-linkage" :key1 "val1" :public-id "foobar-cookie"}
        event-log-double (test-double event-log/write-public-linkage-event)

        expected-event {:type "public-linkage"
                        :key1 "val1"
                        :public-id "foobar-cookie"
                        :munged_public_id "foobar_cookie"
                        :user_id user-id}]

    (with-redefs [event-log/write-public-linkage-event event-log-double]
      (test/testing "event-log/write-public-linkage-event should be called with transformed event"
        (record-public-linkage-event mongo-datastore env request user-id event-body)
        (test/is (= mongo-datastore (:mongo-datastore event-log-double)))
        (test/is (= expected-event (:event event-log-double)))))))