text: const getSpecs = specList => specList ?
    specList.split(',') : [
      'src/**/*.js',
      'tests/**/*.spec.js',
    ];
  
  const getBrowsers = browsers => browsers ?
    browsers.split(',') : [
      'Chrome',
      'Safari'
    ];
  
  module.exports = function (config) {
    config.set({
  
      // base path that will be used to resolve all patterns (eg. files, exclude)
      basePath: '',
  
      // frameworks to use
      // available frameworks: https://npmjs.org/browse/keyword/karma-adapter
      frameworks: ['mocha', 'chai'],
  
      plugins: [
        'karma-mocha-reporter',
        'karma-sourcemap-loader',
        'karma-safari-launcher',
        'karma-chrome-launcher',
        'karma-chai',
        'karma-mocha',
        "karma-webpack"
      ],
  
      // list of files / patterns to load in the browser
      //   e.g.
      //   $ env KARMA_SPECS="tests/foobar.spec.js" $(npm bin)/karma start
      files: getSpecs(process.env.KARMA_SPECS),
  
      // list of files to exclude
      exclude: [],
  
      // preprocess matching files before serving them to the browser
      // available preprocessors: https://npmjs.org/browse/keyword/karma-preprocessor
      preprocessors: {
        'src/**/*.js': ['webpack', 'sourcemap'],
        'tests/**/*.spec.js': ['webpack', 'sourcemap']
      },
  
      webpack: require('./webpack.config'),
  
      // test results reporter to use
      // possible values: 'dots', 'progress'
      // available reporters: https://npmjs.org/browse/keyword/karma-reporter
      reporters: ['mocha'],
  
      mochaReporter: {
        showDiff: true
      },
  
      // web server port
      port: 9876,
  
      // enable / disable colors in the output (reporters and logs)
      colors: true,
  
      // level of logging
      // possible values: config.LOG_DISABLE || config.LOG_ERROR || config.LOG_WARN || config.LOG_INFO || config.LOG_DEBUG
      logLevel: config.LOG_INFO,
  
      // enable / disable watching file and executing tests whenever any file changes
      autoWatch: true,
  
      // start these browsers
      // available browser launchers: https://npmjs.org/browse/keyword/karma-launcher
      browsers: getBrowsers(process.env.KARMA_BROWSERS),
  
      // Continuous Integration mode
      // if true, Karma captures browsers, runs the tests and exits
      singleRun: false,
  
      // Concurrency level
      // how many browser should be started simultaneous
      concurrency: Infinity
    })
  };
  