Refs #4739, add dragDrop utility function to screenshot test page renderer and...

Refs #4739, add dragDrop utility function to screenshot test page renderer and capture alert()'s during screenshot tests.

tests/README.screenshots.md

@@ -166,6 +166,7 @@ The page renderer object has the following methods:
  * **mouseup(selector, [waitTime])**: Sends a mouse up event to the element referenced by `selector`.
  * **sendKeys(selector, keyString, [waitTime])**: Clicks an element to bring it into focus and then simulates typing a string of keys.
  * **sendMouseEvent(type, pos. [waitTime])**: Sends a mouse event by name to a specific position. `type` is the name of an event that phantomjs will recognize. `pos` is a point, eg, `{x: 0, y: 0}`.
+ * **dragDrop(selectorStart, selectorEnd, waitTime)**: Performs a drag/drop of an element (mousedown, mousemove, mouseup) from the element referenced by `selectorStart` and the element referenced by `selectorEnd`.
  * **wait([waitTime])**: Waits without doing anything.
  * **load(url, [waitTime])**: Loads a URL.
  * **reload([waitTime])**: Reloads the current URL.

tests/lib/screenshot-testing/support/page-renderer.js

@@ -95,6 +95,12 @@ PageRenderer.prototype.evaluate = function (impl, waitTime) {
     this.queuedEvents.push([this._evaluate, waitTime, impl]);
 };
 
+PageRenderer.prototype.dragDrop = function (startSelector, endSelector, waitTime) {
+    this.mousedown(startSelector, waitTime);
+    this.mouseMove(endSelector, waitTime);
+    this.mouseup(endSelector, waitTime);
+};
+
 // event impl functions
 PageRenderer.prototype._wait = function (callback) {
     callback();
@@ -380,6 +386,10 @@ PageRenderer.prototype._setupWebpageEvents = function () {
         self.pageLogs.push('Log: ' + message);
     };
 
+    this.webpage.onAlert = function (message) {
+        self.pageLogs.push('Alert: ' + message);
+    };
+
     this.webpage.onLoadStarted = function () {
         self._isLoading = true;
     };