bugfix: fix broken unit test example

src/app.controller.spec.ts

@@ -1,6 +1,7 @@
 import { Test, TestingModule } from '@nestjs/testing';
 import { INestApplication } from '@nestjs/common';
 import { AppController } from './app.controller';
+import { AppService } from './app.service';
 
 describe('AppController', () => {
   let app: TestingModule;
@@ -8,6 +9,7 @@ describe('AppController', () => {
   beforeAll(async () => {
     app = await Test.createTestingModule({
       controllers: [AppController],
+      providers: [AppService],
     }).compile();
   });