testapp/src/app/tabs/tabs-routing.module.ts

import { NgModule } from '@angular/core';
import { RouterModule, Routes } from '@angular/router';
import { TabsPage } from './tabs.page';

const routes: Routes = [
  {
    path:"",pathMatch:"full",redirectTo:"/tabs/tab1"
  },
  {
    path: 'tabs',
    component: TabsPage,
    children: [

      {
        path: 'tab1',
        loadChildren: () => import('../tab1/tab1.module').then(m => m.Tab1PageModule)
      },
      {
        path: 'tab2',
        loadChildren: () => import('../tab2/tab2.module').then(m => m.Tab2PageModule)
      },
      {
        path: 'tab3',
        loadChildren: () => import('../tab3/tab3.module').then(m => m.Tab3PageModule)
      },
      {
        path: 'tab4',
        loadChildren: () => import('../tab4/tab4.module').then( m => m.Tab4PageModule)
      },
     
    ]
  },

];

@NgModule({
  imports: [RouterModule.forChild(routes)],
})
export class TabsPageRoutingModule {}