title: Failing to run tests using Karma
body: <p>I am setting up Karma to simplify unit tests in a legacy project. The problem is, I am getting an error <code>You need to include some adapter that implements __karma__.start method!</code>. As I have found, this is a very non-specific error, so I am at a loss of how to debug it further. I have reduced my setup to the bare minimum, but the error still persists.</p>
  
  <p>Here is the karma config file:</p>
  
  <pre><code>module.exports = function (config) {
    config.set({
      browsers: [ 'PhantomJS' ], //run in Phantom
      autoWatch: false,
      singleRun: true, //just run once by default
      frameworks: [ 'mocha', 'chai', 'sinon', 'chai-sinon' ], // test frameworks
      port: 9876,
      colors: true,
      logLevel: config.LOG_INFO,
      files: [
        './js/test/tests.webpack.js' //just load this file
      ],
      preprocessors: {
        './js/test/tests.webpack.js': [ 'webpack', 'sourcemap' ] //preprocess with webpack and our sourcemap loader
      },
      reporters: [ 'mocha' ], //report results in this format
      webpack: { // webpack settings
        devtool: 'inline-source-map',
        module: {
          loaders: [
            { test: /\.js$/, loader: 'babel-loader' }
          ]
        }
      },
      webpackServer: {
        noInfo: true
      },
      plugins: [
          'karma-mocha',
          'karma-webpack',
          'karma-sourcemap-loader',
          'karma-mocha-reporter',
          'karma-phantomjs-launcher',
          'karma-chai',
          'karma-sinon',
          'karma-chai-sinon'
      ]
    });
  };
  </code></pre>
  
  <p>Here are the packages I have installed (from package.json):</p>
  
  <pre><code>"babel-core": "^6.9.1",
  "babel-loader": "^6.2.4",
  "babel-plugin-module-alias": "^1.5.0",
  "babel-preset-es2015": "^6.9.0",
  "chai": "^3.5.0",
  "karma": "^1.0.0",
  "karma-chai": "^0.1.0",
  "karma-chai-sinon": "^0.1.5",
  "karma-chrome-launcher": "^1.0.1",
  "karma-mocha": "^1.0.1",
  "karma-mocha-reporter": "^2.0.4",
  "karma-phantomjs-launcher": "^1.0.1",
  "karma-sinon": "^1.0.5",
  "karma-sourcemap-loader": "^0.3.7",
  "karma-webpack": "^1.7.0",
  "mocha": "^2.5.3",
  "phantomjs": "^2.1.7",
  "phantomjs-polyfill": "0.0.2",
  "sinon": "^1.17.4",
  "sinon-chai": "^2.8.0",
  "webpack": "^1.13.1"
  </code></pre>
  
  <p>Here is .babelrc:</p>
  
  <pre><code>{
    "presets": ["es2015"]
  }
  </code></pre>
  
  <p>And here is the test file that I am referencing in karma.conf.js (tests.webpack.js). My initial idea was to require all spec files in it, but now I have changed it to run at least a single test. Still no luck:</p>
  
  <pre><code>import chai from 'chai';
  var expect = chai.expect;
  
  console.log('I was found');
  it('works', function () {
      expect(true).to.equal(true);
  })
  </code></pre>
  
  <p>Could you please advise how to debug this problem further?</p>
  
  <p><strong>UPDATE:</strong> Here's a <a href="https://gist.github.com/azangru/9dfde16eb351090c40c33d8214e51985" rel="nofollow">gist</a> with a minimal reproducible case. I must be doing something wrong there, because I am still receiving the error <code>You need to include some adapter that implements __karma__.start method!</code>, but I can't figure out what my mistake is.</p>