code: function createRouter(ClonedVue) {
      var routes = arguments.length > 1 && arguments[1] !== undefined ? arguments[1] : [];
  
      var VueRouter = require('vue-router');
  
      if (typeof VueRouter.default === 'function') {
          VueRouter = VueRouter.default;
      }
  
      ClonedVue.use(VueRouter);
  
      var normalizedRoutes = routes.map(function (route) {
          return typeof route === 'string' ? stubRoute(route) : route;
      });
  
      return new VueRouter({
          mode: 'abstract',
          routes: normalizedRoutes
      });
  }
docs: helper function to create a router instance