Added test for images with wrong extensions.

lib/spriteBackgroundImages.js

@@ -14,7 +14,7 @@ function getCanvasImageFromImageAsset(imageAsset, cb) {
     var canvasImage = new Canvas.Image();
     canvasImage.onerror = function (err) {
         process.nextTick(function () {
-            err.message += ' (' + imageAsset.toString() + ')';
+            err.message += ' (' + imageAsset.urlOrDescription + ')';
             cb(err);
         });
     };
@@ -132,7 +132,7 @@ module.exports = function () {
                 if (cssRule.type !== 1) { // cssom.CSSRule.STYLE_RULE
                     return;
                 }
-                if (('-sprite-selector-for-group') in cssRule.style) {
+                if ('-sprite-selector-for-group' in cssRule.style) {
                     var spriteInfo = extractInfoFromCssRule(cssRule, '-sprite-'),
                         spriteGroupName = spriteInfo.selectorForGroup;
                     if ('location' in spriteInfo) {

test/spriteBackgroundImages.js

@@ -1,5 +1,4 @@
-/*global describe, it*/
-var _ = require('underscore'),
+/*global describe, it*/var _ = require('underscore'),
     expect = require('./unexpected-with-plugins'),
     AssetGraph = require('assetgraph'),
     spriteBackgroundImages = require('../lib/spriteBackgroundImages');
@@ -189,9 +188,27 @@ describe('spriteBackgroundImages', function () {
             })
             .queue(spriteBackgroundImages())
             .queue(function (assetGraph) {
-                expect(assetGraph, 'to contain assets', 'Png');
+                expect(assetGraph, 'to contain asset', 'Png');
                 expect(assetGraph, 'to contain relations', 'CssImage');
             })
             .run(done);
     });
+
+    it('should handle images with wrong extensions', function (done) {
+        new AssetGraph({root: __dirname + '/../testdata/spriteBackgroundImages/imagesWithWrongExtensions/'})
+            .loadAssets('style.css')
+            .populate()
+            .queue(function (assetGraph) {
+                expect(assetGraph, 'to contain asset', 'Png');
+                expect(assetGraph, 'to contain asset', 'Jpeg');
+                expect(assetGraph, 'to contain relations', 'CssImage', 2);
+            })
+            .queue(spriteBackgroundImages())
+            .queue(function (assetGraph) {
+                expect(assetGraph, 'to contain asset', 'Png');
+                expect(assetGraph, 'to contain no asset', 'Jpeg');
+                expect(assetGraph, 'to contain relations', 'CssImage', 2);
+            })
+            .run(done);
+    });
 });

testdata/spriteBackgroundImages/imagesWithWrongExtensions/style.css

@@ -0,0 +1,7 @@
+body {
+    background-image: url(actuallyAJpeg.png?sprite=foo);
+}
+
+.quux {
+    background-image: url(actuallyAPng.jpg?sprite=foo);
+}