feature: make typescript starter more robust

src/app.controller.spec.ts

@@ -0,0 +1,20 @@
+import { Test, TestingModule } from '@nestjs/testing';
+import { INestApplication } from '@nestjs/common';
+import { AppController } from './app.controller';
+
+describe('AppController', () => {
+  let app: TestingModule;
+
+  beforeAll(async () => {
+    app = await Test.createTestingModule({
+      controllers: [AppController],
+    }).compile();
+  });
+
+  describe('root', () => {
+    it('should return "Hello World!"', () => {
+      const appController = app.get<AppController>(AppController);
+      expect(appController.root()).toBe('Hello World!');
+    });
+  });
+});