Add optional support for code-coverage of generated code

[uglow]

Fixes #22

Example output from Webpack + Karma + karma-coverage:

--------------------------|----------|----------|----------|----------|----------------|
File                      |  % Stmts | % Branch |  % Funcs |  % Lines |Uncovered Lines |
--------------------------|----------|----------|----------|----------|----------------|
 notifications/           |    70.76 |     28.4 |    77.78 |    72.61 |                |
  notification.html       |    73.12 |       30 |    76.92 |    74.16 |... 155,156,157 |
  notificationsPanel.html |    67.95 |    27.45 |    78.57 |    70.59 |... 159,161,162 |
  statuses.js             |      100 |      100 |      100 |      100 |                |
  types.js                |      100 |      100 |      100 |      100 |                |
--------------------------|----------|----------|----------|----------|----------------|
All files                 |    70.76 |     28.4 |    77.78 |    72.61 |                |
--------------------------|----------|----------|----------|----------|----------------|

karma.config.js:

// Global karma config
'use strict';

const DefinePlugin = require('webpack').DefinePlugin;   // Needed to pass the testFilesRegEx to test.files.js
let testFilesRegEx = /unitTest\/.*spec\.(js|jsx)$/;

// Customise the testFilesRegEx to filter which files to test, if desired.
// Remember to also update .babelrc

// We want to re-use the loaders from the dev.webpack.config
let webpackConfig = require('./../webpack/dev.webpack.config.js');
let preprocessorList = ['webpack', 'sourcemap'];

let karmaConfig = {
  autoWatch: true,

  // base path, that will be used to resolve files and exclude
  basePath: '../../',

  // testing framework to use (jasmine/mocha/qunit/...)
  frameworks: ['jasmine'],

  // list of files / patterns to exclude
  exclude: [],

  // web server default port
  port: 8081,

  // Start these browsers, currently available:
  // - Chrome, ChromeCanary, Firefox, Opera, Safari (only Mac), PhantomJS, IE (only Windows)
  browsers: [
    'PhantomJS'
  ],

  plugins: [
    'karma-phantomjs-launcher',
    'karma-jasmine',
    'karma-junit-reporter',
    'karma-coverage',
    'karma-chrome-launcher',
    require('karma-webpack'),
    'karma-sourcemap-loader',
    'karma-threshold-reporter'
  ],

  files: [
    'node_modules/phantomjs-polyfill/bind-polyfill.js',
    'node_modules/phantomjs-polyfill-object-assign/object-assign-polyfill.js',
    'config/testUnit/test.files.js'
  ],

  preprocessors: {
    'config/testUnit/test.files.js': preprocessorList
  },

  reporters: ['progress', 'junit', 'coverage', 'threshold'],

  coverageReporter: {
    dir: 'reports/coverage/',
    reporters: [
      { type: 'cobertura', subdir: 'cobertura' },
      { type: 'lcovonly', subdir: 'lcov' },
      { type: 'html', subdir: 'html' },
      { type: 'json', subdir: 'json' },
      { type: 'text' }
    ],
    // --------------------- Extra config required (start) -------------------------
    // A custom report collector for Svelte HTML components, so that source maps display for generated code
    _onWriteReport: function(collector) {
      // Iterate over the keys of the collector.
      // If the collector key is a HTML file, do this: coverage.code = coverage.inputSourceMap.code
      var store = collector.store;
      var keys = store.keys().filter(function(key) {
        return /\.html$/.test(key);
      });

      keys.forEach(function(key) {
        let coverage = store.getObject(key);

        if (coverage.inputSourceMap) {
          // Replace the existing key with one that has the code property
          coverage.code = coverage.inputSourceMap.sourcesContent[0].split(/(?:\r?\n)|\r/);
          store.set(key, JSON.stringify(coverage))
        }
      });

      return collector;
    }
    // --------------------- Extra config required (end) -------------------------
  },

  junitReporter: {
    outputDir: 'reports/unit/'
  },

  thresholdReporter: require('./thresholds.json'),

  // Webpack please don't spam the console when running in karma!
  webpackMiddleware: { stats: 'errors-only'},

  singleRun: false,
  colors: true
};

webpackConfig.plugins.push(new DefinePlugin({
  __karmaTestSpec: testFilesRegEx
}));

// Change devtool to allow the sourcemap loader to work: https://github.com/webpack/karma-webpack
webpackConfig.devtool = 'inline-source-map';

// Turn off performance hints
webpackConfig.performance.hints = false;

karmaConfig.webpack = webpackConfig;

module.exports = karmaConfig;

[uglow]

@Rich-Harris What do we do with this? I need code-coverage reports to work with Svelte & non-Svelte code.

[uglow]

Bump