Webpack + Mocha + Chai

karma.config.js

var webpackConfig = require('./webpack.config');
webpackConfig.devtool = 'inline-source-map';

module.exports = function (config) {
  config.set({
    browsers: [ 'PhantomJS' ],
    singleRun: true,
    frameworks: [ 'mocha', 'chai', 'sinon', 'sinon-chai' ],
    files: [
      '*/*.spec.js'
    ],
    plugins: [
      'karma-phantomjs-launcher',
      'karma-chai',
      'karma-mocha',
      'karma-sourcemap-loader',
      'karma-webpack',
      'karma-mocha-reporter',
      'karma-sinon',
      'karma-sinon-chai'
    ],
    preprocessors: {
      'tests.webpack.js': [ 'webpack', 'sourcemap' ]
    },
    reporters: [ 'mocha' ],
    webpack: webpackConfig,
    webpackServer: {
      noInfo: true
    },
    autoWatch: true
  });
};

packge.json

{
  "name": "webpack_mocha_chai2",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
 "scripts": {
  "dev": "WEBPACK_ENV=dev ./node_modules/.bin/webpack --watch --inline",
  "build": "WEBPACK_ENV=build ./node_modules/.bin/webpack",
  "test": "karma start",
  "test:ci": "watch 'npm run test' src/"
},
  "author": "Veeresh Meesala",
  "license": "MIT",
  "devDependencies": {
    "babel-core": "^6.24.0",
    "babel-eslint": "^7.2.1",
    "babel-loader": "^6.4.1",
    "chai": "^3.5.0",
    "core-js": "^2.4.1",
    "eslint": "^3.18.0",
    "eslint-loader": "^1.7.0",
    "eslint-plugin-react": "^6.10.3",
    "karma": "^1.5.0",
    "karma-chai": "^0.1.0",
    "karma-chai-plugins": "^0.8.0",
    "karma-chai-sinon": "^0.1.5",
    "karma-chrome-launcher": "^2.0.0",
    "karma-mocha": "^1.3.0",
    "karma-mocha-reporter": "^2.2.3",
    "karma-phantomjs-launcher": "^1.0.4",
    "karma-sinon": "^1.0.5",
    "karma-sinon-chai": "^1.2.4",
    "karma-sourcemap-loader": "^0.3.7",
    "karma-webpack": "^2.0.3",
    "react": "^15.4.2",
    "watch": "^1.0.2",
    "webpack": "^2.3.2",
    "webpack-dev-server": "^2.4.2"
  }
}

webpack.config.js

var WebpackDevServer = require('webpack-dev-server');
var env = process.env.WEBPACK_ENV;
var UglifyJsPlugin = webpack.optimize.UglifyJsPlugin;
var plugins = [];

plugins.push(new UglifyJsPlugin({ minimize: true }));

var host = '0.0.0.0';
var port = '9000';

var config = {
  entry: './src/index.js',
  devtool: 'source-map',
   output: {
    path: __dirname + '/lib',
    filename: outputFile,
    publicPath: __dirname + '/example'
  },
 module: {
    loaders: [
      {
        test: /(\.jsx|\.js)$/,
        loader: 'babel',
        exclude: /(node_modules|bower_components)/
      },
      {
      test: /(\.jsx|\.js)$/,
      loader: "eslint-loader",
      exclude: /node_modules/
    }
    ]
  },
  plugins: plugins
};

if (env === 'dev') {
  new WebpackDevServer(webpack(config), {
    contentBase: './example',
    hot: true,
    debug: true
  }).listen(port, host, function (err, result) {
    if (err) {
      console.log(err);
    }
  });
  console.log('-------------------------');
  console.log('Local web server runs at http://' + host + ':' + port);
  console.log('-------------------------');
}

module.exports = config;