How to use the @ionic/angular.IonicAngularModule.forRoot function in @ionic/angular

import { AppRoutingModule } from './app-routing.module';
import { AppComponent } from './app.component';

import { ConferenceData } from './providers/conference-data';
import { UserData } from './providers/user-data';

@NgModule({
  declarations: [
    AppComponent,
  ],
  imports: [
    AppRoutingModule,
    BrowserModule,
    HttpModule,
    IonicAngularModule.forRoot(),
    IonicStorageModule.forRoot(),
    IonicRouterModule.forRoot(),
  ],
  providers: [
    ConferenceData,
    InAppBrowser,
    SplashScreen,
    UserData
  ],
  bootstrap: [AppComponent],
  schemas: [
    CUSTOM_ELEMENTS_SCHEMA
  ]
})
export class AppModule { }

import { CUSTOM_ELEMENTS_SCHEMA, NgModule } from '@angular/core';
import { HttpClientModule } from '@angular/common/http';

import { AppComponent } from './app.component';
import { AppRoutingModule } from './app-routing.module';
import { PostTestService } from './post-test/post-test.service';

import { IonicAngularModule, IonicRouterModule } from '@ionic/angular';

@NgModule({
  declarations: [AppComponent],
  imports: [
    AppRoutingModule,
    BrowserModule,
    HttpClientModule,
    IonicAngularModule.forRoot(),
    IonicRouterModule.forRoot()
  ],
  bootstrap: [AppComponent],
  schemas: [CUSTOM_ELEMENTS_SCHEMA],
  providers: [PostTestService]
})
export class AppModule { }

import { CUSTOM_ELEMENTS_SCHEMA, NgModule } from '@angular/core';
import { HttpClientModule } from '@angular/common/http';

import { AppComponent } from './app.component';
import { AppRoutingModule } from './app-routing.module';
import { PostTestService } from './post-test/post-test.service';

import { IonicAngularModule } from '@ionic/angular';

@NgModule({
  declarations: [AppComponent],
  imports: [
    AppRoutingModule,
    BrowserModule,
    HttpClientModule,
    IonicAngularModule.forRoot(),
  ],
  bootstrap: [AppComponent],
  schemas: [CUSTOM_ELEMENTS_SCHEMA],
  providers: [PostTestService]
})
export class AppModule { }

async(() => {
      TestBed.configureTestingModule({
        declarations: [BasicInputsPageComponent],
        imports: [FormsModule, IonicAngularModule.forRoot()],
        schemas: [CUSTOM_ELEMENTS_SCHEMA]
      }).compileComponents();
    })
  );