Karma Unit Test case coverage for lazy loading in Angular 8

How to write the unit test cases for lazy loading in angular 8. i tried a lot but my unit test cases are not covering "loadChildren" routing.

import { Routes, RouterModule } from "@angular/router"; import { AppRoutingComponent } from "./app-routing.component";

const appRoutes: Routes = [

{ path: "index.html", component: AppRoutingComponent },

{ path: "product", loadChildren: () => import('app/dashboard/product.module').then(m => m.ProductModule) },

{ path: "", redirectTo: "/main", pathMatch: "full" } ];

export const routedComponents = [ AppRoutingComponent,

];

@NgModule({
imports: [routing], exports: [RouterModule]

})

export class AppRoutingModule { }

Please provide some guidance.

Thanks in advance.