code: function(size, name) {
      var fs = require('fs');
      var path = require('path');
      name = this.uniqueName(name);
      // Cannot set this as a world property because the world
      // is cleaned up before the AfterFeatures hook is fired.
      var fixturePath = path.resolve('./features/extra/fixtures/tmp');
      if (!fs.existsSync(fixturePath)) fs.mkdirSync(fixturePath);
      var filename = path.join(fixturePath, name);
      var body;
      if (typeof size === 'string') {
        switch (size) {
          case 'empty': body = new Buffer(0); break;
          case 'small': body = new Buffer(1024 * 1024); break;
          case 'large': body = new Buffer(1024 * 1024 * 20); break;
        }
      } else if (typeof size === 'number') {
        body = new Buffer(size);
      }
  
      fs.writeFileSync(filename, body);
      return filename;
    }
docs: Creates a fixture file of given size and returns the path.