wrap-cookies no longer overwrites any pre-set Set-Cookie headers

@@ -115,9 +115,10 @@
   "Add a Set-Cookie header to a response if there is a :cookies key."
   [response]
   (if-let [cookies (:cookies response)]
-    (assoc-in response
-              [:headers "Set-Cookie"]
-              (write-cookies cookies))
+    (update-in response
+               [:headers "Set-Cookie"]
+               concat
+               (write-cookies cookies))
     response))
 
 (defn wrap-cookies

@@ -71,3 +71,10 @@
         resp    ((wrap-cookies handler) {})]
     (is (= {"Set-Cookie" (list "a=hello+world")}
            (:headers resp)))))
+
+(deftest wrap-cookies-keep-set-cookies-intact
+  (let [handler (constantly {:headers {"Set-Cookie" (list "a=b")}
+                             :cookies {:c "d"}})
+        resp    ((wrap-cookies handler) {})]
+    (is (= {"Set-Cookie" (list "a=b" "c=d")}
+           (:headers resp)))))