add phantomJS to karma config

config/karma.config.js

@@ -6,6 +6,7 @@ var ROOT_PATH = path.resolve(__dirname, '..');
 module.exports = function(config) {
   config.set({
     basePath: ROOT_PATH,
+    browsers: ['PhantomJS'],
     frameworks: ['jasmine'],
     files: [
       { pattern: 'spec/javascripts/test_bundle.js', watched: false },

package.json

@@ -41,6 +41,7 @@
     "jasmine-jquery": "^2.1.1",
     "karma": "^1.3.0",
     "karma-jasmine": "^1.1.0",
+    "karma-phantomjs-launcher": "^1.0.2",
     "karma-sourcemap-loader": "^0.3.7",
     "karma-webpack": "^1.8.0"
   }