enable linting during test dev

build/karma.dev.config.js

@@ -1,6 +1,15 @@
 var base = require('./karma.base.config.js')
 
 module.exports = function (config) {
+  // enable linting during dev
+  base.webpack.module.preLoaders =  [
+    {
+      test: /\.js$/,
+      loader: 'eslint',
+      exclude: /node_modules/
+    }
+  ]
+
   config.set(Object.assign(base, {
     browsers: ['Chrome'],
     reporters: ['progress']