Create a wrapper around createElement('img') so it can be tested

I have no idea how to get sinon to actually stub
`document.createElement(‘img’)` and every attempt causes Phantom to
stop responding.

This was the easiest way out. I’m sorry.

This is a test backfilled for #334

Author: mattrobenolt

src/raven.js

@@ -717,7 +717,7 @@ function send(data) {
 
 
 function makeRequest(data) {
-    var img = document.createElement('img'),
+    var img = newImage(),
         src = globalServer + authQueryString + '&sentry_data=' + encodeURIComponent(JSON.stringify(data));
 
     img.crossOrigin = 'anonymous';
@@ -736,6 +736,13 @@ function makeRequest(data) {
     img.src = src;
 }
 
+// Note: this is shitty, but I can't figure out how to get
+// sinon to stub document.createElement without breaking everything
+// so this wrapper is just so I can stub it for tests.
+function newImage() {
+    return document.createElement('img');
+}
+
 function isSetup() {
     if (!hasJSON) return false;  // needs JSON support
     if (!globalServer) {

test/raven.test.js

@@ -24,11 +24,6 @@ function flushRavenState() {
     Raven.uninstall();
 }
 
-var imageCache = [];
-window.Image = function Image() {
-    imageCache.push(this);
-};
-
 // window.console must be stubbed in for browsers that don't have it
 if (typeof window.console === 'undefined') {
     console = {error: function(){}};
@@ -1045,9 +1040,10 @@ describe('globals', function() {
 
     describe('makeRequest', function() {
         it('should load an Image', function() {
-            imageCache = [];
             authQueryString = '?lol';
             globalServer = 'http://localhost/';
+            var imageCache = [];
+            this.sinon.stub(window, 'newImage', function(){ var img = {}; imageCache.push(img); return img; });
 
             makeRequest({foo: 'bar'});
             assert.equal(imageCache.length, 1);
@@ -1625,7 +1621,9 @@ describe('Raven (public API)', function() {
         });
 
         it('should work as advertised #integration', function() {
-            imageCache = [];
+            var imageCache = [];
+            this.sinon.stub(window, 'newImage', function(){ var img = {}; imageCache.push(img); return img; });
+
             setupRaven();
             Raven.captureMessage('lol', {foo: 'bar'});
             assert.equal(imageCache.length, 1);