Add clear method for Cache.

Change-Id: I7cf64ff04d162225b40e76f6b7abfd56e92e883a

src/main/om/next/cache.cljs

@@ -10,7 +10,11 @@
         (swap! index assoc id x')))
     (.push arr id))
   (get [this id]
-    (get @index id)))
+    (get @index id))
+  (clear [this]
+    (reset! (.-index this) {})
+    (set! (.-arr this) #js [])
+    this))
 
 (defn cache [size]
   (Cache. #js [] (atom {}) size))

src/test/om/next/tests.cljc

@@ -1057,6 +1057,27 @@
     (is (not (contains? (get t-err 'this/throws) :result)))
     (is (= (get (om/transact! r '[(this/throws) :app/count]) :app/count) 2))))
 
+#?(:cljs
+   (deftest test-cache-clear
+     (let [r (om/reconciler {:state (atom {:app/count 0})
+                             :parser p})
+           h (get-in r [:config :history])]
+       (is (= 0 (count @(.-index h))))
+       (is (= 0 (count (.-arr h))))
+       (om/transact! r '[(app/inc!)])
+       (let [h (get-in r [:config :history])]
+         (is (= 1 (count @(.-index h))))
+         (is (= 1 (count (.-arr h)))))
+       (let [r' (update-in r [:config :history] #(.clear %))
+             h' (get-in r' [:config :history])]
+         (is (= {} @(.-index h')))
+         (is (= 0 (count (.-arr h'))))
+         (is (= [] (js->clj (.-arr h')))))
+       (om/transact! r '[(app/inc!)])
+       (let [h (get-in r [:config :history])]
+         (is (= 1 (count @(.-index h))))
+         (is (= 1 (count (.-arr h))))))))
+
 ;; -----------------------------------------------------------------------------
 ;; Recursive Parsing