title: Karma+Mocha+React Cannot convert a Symbol value to a string
body: <p>I am using webpack+babel for a React+Redux app and Mocha+Karma for testing. The redux test cases are getting executed properly. However, when I try to do DOM testing using react-addons-test-utils and running it with Karma it gives this error </p>
  
  <p>Uncaught TypeError: Cannot convert a Symbol value to a string
    at <a href="http://localhost:9876/karma.js:339">http://localhost:9876/karma.js:339</a></p>
  
  <p>In order to debug it properly I put a couple of loggers in karma lib files( I know I shouldn't have) and got this</p>
  
  <p><a href="http://i.stack.imgur.com/O2IWs.png">Karma Error for React DOM testing</a></p>
  
  <p>However, when I do not use KarmaJS and simply try to run the tests, it seems fine. Here is my karma.conf </p>
  
  <pre><code>"use strict";
  let webpackConfig = require('./webpack.config');
  const coverage = process.env.COVERAGE;
  
  webpackConfig.externals = {};
  
  getWebpackLoaders();
  
  module.exports = function(config){
    config.set({
      basePath: '.',
      frameworks:['mocha'],
      autoWatchBatchDelay:500,
      browsers: ['Chrome'],
      customLaunchers: {
        Chrome_without_security: {
          base: 'Chrome',
          flags: ['--disable-web-security']
        }
      },
      preprocessors: {
        './test/**/*.js':['webpack']
      },
      reporters: getReporters(),
      coverageReporter: {
        reporters: [
          {type: 'lcov', dir: 'coverage/', subdir: '.'},
          {type: 'json', dir: 'coverage/', subdir: '.'},
          {type: 'text-summary'}
        ]
      },
      exclude:['node_modules'],
      port:9876,
  
      files: [
        'node_modules/react/dist/react-with-addons.js',
        'test/test.js'
      ],
      webpack:webpackConfig,
      plugins: [
        'karma-webpack',
        'karma-mocha',
        'karma-coverage',
        'karma-chrome-launcher'
      ]
    })
  };
  
  function getWebpackLoaders(){
    if(coverage){
      let loaders  = webpackConfig.module.loaders;
      let jsLoader = loaders[1];
      jsLoader.exclude = /node_modules|\.test\.js$/ //exclude both node_modules and test
      loaders.push({
        test:/\.test\.js$/,
        loaders:['babel-loader']
      });
      loaders.push({
        test: /\.js$/,
        loaders: ['isparta'],
        exclude: /node_modules|\.test.js$/ // exclude node_modules and test files
      })
    }
  }
  
  function getReporters() {
    var reps = ['progress'];
    if (coverage) {
      reps.push('coverage');
    }
    return reps;
  }
  </code></pre>
  
  <p>EDIT 1. Adding webpack.config to this</p>
  
  <pre><code>var webpack = require('webpack');
  var argv = require('minimist')(process.argv.slice(2));
  
  var DEBUG = !argv.release;
  
  var AUTOPREFIXER_LOADER = 'autoprefixer-loader?{browsers:[' +
    '"Android &gt;= 4", "Chrome &gt;= 20", "Firefox &gt;= 24", ' +
    '"Explorer &gt;= 9", "iOS &gt;= 6", "Safari &gt;= 6"]}';
  
  var GLOBALS = {
    'process.env.NODE_ENV': DEBUG ? '"development"' : '"production"',
    '__DEV__': DEBUG
  };
  
  var config = {
  
    entry: './app.js',
  
    output: {
      filename: 'app.js',
      path: './build/',
      publicPath: './',
      sourcePrefix: '  '
    },
  
    externals: {
      react: 'React'
    },
  
    cache: DEBUG,
    debug: DEBUG,
    devtool: DEBUG ? '#inline-source-map' : false,
  
    stats: {
      colors: true,
      reasons: DEBUG
    },
  
    plugins: [
      new webpack.optimize.OccurenceOrderPlugin(),
      new webpack.DefinePlugin(GLOBALS)
    ].concat(DEBUG ? [] : [
      new webpack.optimize.DedupePlugin(),
      new webpack.optimize.UglifyJsPlugin(),
      new webpack.optimize.AggressiveMergingPlugin()
    ]),
  
    resolve: {
      extensions: ['', '.webpack.js', '.js', '.jsx']
    },
  
    module: {
      preLoaders: [
        {
          test: /\.js$/,
          exclude: /node_modules/,
          loader: 'eslint-loader'
        }
      ],
  
      loaders: [
        {
          test: /\.less$/,
          loader: 'style-loader!css-loader!' + AUTOPREFIXER_LOADER + '!less-loader'
        },
        {
          test: /\.jsx?$/,
          exclude: /node_modules/,
          loader: 'babel-loader'
        },
        {
          test: /\.json$/,
          exclude: /node_modules/,
          loader: 'json-loader'
        }
      ]
    }
  };
  
  module.exports = config;
  </code></pre>