Add tests for sk.object functions and sk.stateReflector.

js/tests/stateReflector.js

+describe('sk.stateReflector',
+  function() {
+    var clock;
+
+    afterEach(function () { if (clock) { clock.restore(); } });
+
+    function testStateReflector() {
+      clock = sinon.useFakeTimers();
+      var page = {
+        state: {
+          height: 2.0,
+          name: "Fritz",
+          alive: true,
+          labels: "foo bar baz",
+        }
+      };
+
+      var initHistoryLength = window.history.length;
+      var spy = sinon.spy();
+      var nextResolveCallback;
+      var pending = new Promise(function(resolve, reject) {
+        nextResolveCallback = resolve;
+        var callback = function() {
+          spy();
+          nextResolveCallback();
+        };
+        sk.stateReflector(page, callback);
+        // Fake the polymer-ready event.
+        window.dispatchEvent(new Event('polymer-ready'));
+      }).then(function() {
+        assert.equal(spy.callCount, 1);
+        page.state.height = 1.5;
+        page.state.name = "Lucy";
+        clock.tick(200);  // Causes timers to be called.
+        assert.equal(window.history.length - initHistoryLength, 1);
+        page.state.alive = false;
+        page.state.labels = "foo bar";
+        clock.tick(200);  // Causes timers to be called.
+        assert.equal(window.history.length - initHistoryLength, 2);
+        assert.deepEqual(page.state,
+                         { height: 1.5,
+                           name: "Lucy",
+                           alive: false,
+                           labels: "foo bar" });
+        // Trigger popstate due to history.back() and wait for callback.
+        return new Promise(function (resolve, reject) {
+          nextResolveCallback = resolve;
+          window.history.back();
+        });
+      }).then(function() {
+        assert.equal(spy.callCount, 2);
+        assert.deepEqual(page.state,
+                         { height: 1.5,
+                           name: "Lucy",
+                           alive: true,
+                           labels: "foo bar baz" });
+        // Trigger popstate due to history.back() and wait for callback.
+        return new Promise(function (resolve, reject) {
+          nextResolveCallback = resolve;
+          window.history.back();
+        });
+      }).then(function() {
+        assert.equal(spy.callCount, 3);
+        assert.deepEqual(page.state,
+                         { height: 2.0,
+                           name: "Fritz",
+                           alive: true,
+                           labels: "foo bar baz" });
+        // Trigger popstate due to history.forward() and wait for callback.
+        return new Promise(function (resolve, reject) {
+          nextResolveCallback = resolve;
+          window.history.forward();
+        });
+      }).then(function() {
+        assert.equal(spy.callCount, 4);
+        assert.deepEqual(page.state,
+                         { height: 1.5,
+                           name: "Lucy",
+                           alive: true,
+                           labels: "foo bar baz" });
+      });
+      return pending;
+    }
+
+    it("should link browser history with a JS object's state",
+       testStateReflector);
+  }
+);