Core async fake timeout

fake_timeout.clj

(defrecord FakeTimeout [current-time time-chans])

(defn timeout-fn
  [{:keys [current-time time-chans]}]
  (fn [time]
    (let [ch (async/chan)]
      (swap! time-chans merge-with into {(+ @current-time time) #{ch}})
      (println time-chans)
      ch)))

(defn fast-forward [{:keys [current-time time-chans]} elapsed]
  (let [end-time (swap! current-time + elapsed)
        affected (sort < (filter <= (keys @time-chans)))]
    (doseq [timeindex affected]
      (doseq [ch (get time-chans timeindex)] (async/close! ch))
      (swap! time-chans dissoc timeindex))))

(defn fake-timeout-factory [] (->FakeTimeout (atom 0) (atom {})))

usage.clj

(def fakeout (fake-timeout-factory))

(with-redefs [async/timeout (timeout-fn fakeout)]
  (async/go (async/<! (async/timeout 2000)) (println "Hi")))

;... Wait more than two seconds, expect no "Hi"

(fast-forward fakeout 3000)
; Expect "Hi" immediately