Add tests for undo behaviour

Inspired by #149, this adds tests to cover the change that was made. It
also tests the redo logic.

src/re_frame/undo.cljs

@@ -164,7 +164,7 @@
 
 
 (handlers/register-base     ;; not a pure handler
-  :purge-redos              ;; usage:  (dispatch [:purge-redo])
+  :purge-redos              ;; usage:  (dispatch [:purge-redos])
   (fn handler
     [_ _]
     (if-not (redos?)

test/re-frame/test/test_runner.cljs

@@ -1,9 +1,11 @@
 (ns re-frame.test.runner
   (:require [jx.reporter.karma :as karma :include-macros true]
-            [re-frame.test.middleware]))
+            [re-frame.test.middleware]
+            [re-frame.test.undo]))
 
 
 (defn ^:export run [karma]
   (karma/run-tests
     karma
-    're-frame.test.middleware))
+    're-frame.test.middleware
+    're-frame.test.undo))

test/re-frame/test/undo.cljs

@@ -0,0 +1,45 @@
+(ns re-frame.test.undo
+  (:require [cljs.test :refer-macros [is deftest]]
+            [re-frame.undo :as undo]
+            [re-frame.db :as db]
+            [re-frame.core :as re-frame]))
+
+(deftest test-undos
+  ;; Create undo history
+  (undo/set-max-undos! 5)
+  (doseq [i (range 10)]
+    (reset! db/app-db i)
+    (undo/store-now! i))
+
+  ;; Check the undo state is correct
+  (is (undo/undos?))
+  (is (not (undo/redos?)))
+  (is (= [4 5 6 7 8 9] (undo/undo-explanations)))
+  (is (= [5 6 7 8 9] @undo/undo-list))
+
+  ;; Undo the actions
+  (re-frame/dispatch-sync [:undo])
+  (is (= @db/app-db 9))
+  (is (undo/redos?))
+  (re-frame/dispatch-sync [:undo])
+  (is (= @db/app-db 8))
+  (re-frame/dispatch-sync [:undo])
+  (is (= @db/app-db 7))
+  (re-frame/dispatch-sync [:undo])
+  (is (= @db/app-db 6))
+  (re-frame/dispatch-sync [:undo])
+  (is (= @db/app-db 5))
+  (is (not (undo/undos?)))
+  (is (undo/redos?))
+
+  ;; Redo them again
+  (re-frame/dispatch-sync [:redo 5])
+  (is (= @db/app-db 9))
+  (is (not (undo/redos?)))
+  (is (undo/undos?))
+  (is (= [5 6 7 8 9] @undo/undo-list))
+
+  ;; Clear history
+  (undo/clear-history!)
+  (is (not (undo/undos?)))
+  (is (not (undo/redos?))))