title: How do I add code coverage to Typescript + Webpack + Karma w/ Istanbul-Instrumenter
body: <p>I have created a simple <a href="https://github.com/jrgleason/webpack-karma-coverage-demo" rel="nofollow noreferrer">Webpack + Typescript + Karma</a> app but I am having trouble getting the code coverage to work properly. Per projects like <a href="https://github.com/AngularClass/angular2-webpack-starter" rel="nofollow noreferrer">this</a> and the other info provided <a href="https://stackoverflow.com/questions/39570980/karma-coverage-report-combined-with-webpack">here</a> you can see I tried...</p>
  
  <pre><code>// In test bundle
  const componentsContext = require.context('../src/', true, /\.js$/);
  componentsContext.keys().forEach(componentsContext);
  
  // In webpack config
  const helpers = require('./helpers.js')
  const webpackMerge = require('webpack-merge'); // used to merge webpack configs
  const commonConfig = require('./webpack.common.js'); // the settings that are common to prod and dev
  const HtmlWebpackPlugin = require('html-webpack-plugin');
  module.exports = function () {
    return webpackMerge(commonConfig(), {
      devtool: 'inline-source-map',
      output: {
          path: helpers.root("dist"),
          filename: '[name].bundle.js',
      },
      module: {
        postLoaders: [
          {
            test: /^((?!\.spec\.ts).)*.ts$/,
            exclude: /(node_modules|bower_components)/,
            loader: 'istanbul-instrumenter'
          }
        ]
      }
    })
  };
  </code></pre>
  
  <p>but when I run <code>karma start test/karma.conf.js</code> I see 100% and no files listed. What am I missing?</p>