my-chat-room/apps/chat-room/src/app/app.component.spec.ts

import { TestBed, waitForAsync } from '@angular/core/testing';
import { HttpClientModule } from '@angular/common/http';
import { FormsModule } from '@angular/forms';
import { MockService } from 'ng-mocks';
import { AppComponent } from './app.component';
import { MessagesService } from './messages.service';
import { of } from 'rxjs';

describe('AppComponent', () => {
  beforeEach(
    waitForAsync(() => {
      TestBed.configureTestingModule({
        declarations: [AppComponent],
        imports: [HttpClientModule, FormsModule],
        providers: [
          { provide: MessagesService, useValue: MockService(MessagesService) },
        ],
      }).compileComponents();
    })
  );

  beforeEach(() => {
    const messageService = TestBed.inject(MessagesService);
    jest.spyOn(messageService, 'getMessages').mockReturnValue(of([]));
  });

  it('should create the app', () => {
    const fixture = TestBed.createComponent(AppComponent);
    const app = fixture.debugElement.componentInstance;
    expect(app).toBeTruthy();
  });
});