Using `with-redefs` to redef a function that's called inside a go block

with-redefs-and-go.cljs

; ---------------------------------------------------------------------------------
; handler code
; ---------------------------------------------------------------------------------

; My handler code fetches messages in parrallel and then picks them off of the channel
; vector within the go block. I've succesfully redef'ed `http/get` by bringing it out 
; of the `go` block, but redef'ing 're-frame/dispatch` doesn't seem to be working.

(defn fetch-full-messages [db [scenario-name]]
  (if-let [scenario (get-in db [:admin-configuration :scenarios scenario-name])]
    (letfn [(fetch-full-message-by-id [message-id]
              (http/get (str (form-full-base-url db) "Messages/" message-id) {:with-credentials? false :basic-auth (form-credentials-map db)}))]
      (let [message-ids (map #(get-in % [:body :messageId]) (:messages scenario))
            channels (mapv fetch-full-message-by-id message-ids)]
        (go
          (let [responses (loop [responses []                  ; definitely could refactor this into a reduce (I was a less
                                 remaining-channels channels]  ;  seasoned clojurescript developer when I wrote this)
                            (if (empty? remaining-channels)
                              responses
                              (recur (conj responses (<! (first remaining-channels))) (vec (rest remaining-channels)))))]
            (if (every? has-success-status? responses)
              (do
                (re-frame/dispatch [:save-fetched-messages responses])
                (re-frame/dispatch [:form-broadcast-instructions]))
              (js/alert "Error: Unsuccessful fetch of at least one message in scenario.  Not able to proceed"))))))
    (nav/set-location! "/"))
  db)

; ---------------------------------------------------------------------------------
; test
; ---------------------------------------------------------------------------------

; Not a proper test ofcourse since I'm not asserting anything, but I'm trying to 
; figure out why my `re-frame/dispatch` redef is not working. 

(deftest temp-test
  (cljs.test/async done
    (with-redefs [http/get (fn [url]
                             (let [chan (chan)]
                               (async/put! chan {:status 200 :url url})
                               chan))
                  re-frame/dispatch (fn [] (print "dispatching now"))]
                 (handler/fetch-full-messages @db ["test"])
                 (done))))