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