Export functions from main.ts and create test code

src/main.spec.ts

@@ -0,0 +1,66 @@
+import { NestFactory } from '@nestjs/core';
+import { INestApplication } from '@nestjs/common';
+import { SwaggerModule, OpenAPIObject, SwaggerCustomOptions } from '@nestjs/swagger';
+
+jest.mock('@nestjs/core');
+
+interface DocumentationConfig {
+  title: string;
+  description: string;
+  version: string;
+  endpoint: string;
+}
+
+describe('Main', () => {
+  it('should creates a NestFactory', async () => {
+    const listenSpy = jest.fn();
+    const createSpy = Promise.resolve({
+      listen: listenSpy,
+    }) as unknown as Promise<INestApplication>;
+
+    jest.spyOn(NestFactory, 'create').mockImplementation(() => createSpy);
+
+    const bootstrap = require('./main').bootstrap;
+    await bootstrap();
+    expect(listenSpy).toHaveBeenCalledTimes(2);
+    expect(listenSpy).toHaveBeenCalledWith(3000);
+  });
+
+  it('should correctly initialize swagger API documentation', () => {
+    const nestApp = {};
+    const swaggerDocument = {};
+    SwaggerModule.createDocument = jest.fn().mockReturnValue(swaggerDocument);
+    SwaggerModule.setup = jest.fn();
+
+    const documentConfig: DocumentationConfig = {
+      title: 'Driver License Verification API',
+      description: 'An unofficial driver license verification crawler API service with live status check support.',
+      version: 'Alpha',
+      endpoint: 'docs',
+    };
+
+    const customConfig: SwaggerCustomOptions = {
+      customCss: `
+      .topbar { display: none; }
+      .swagger-ui { padding-top: 50px; }`,
+      customSiteTitle: 'Driver License Verification API',
+    };
+
+    const setupDocument = require('./main').setupDocument;
+
+    setupDocument(nestApp);
+
+    expect(SwaggerModule.createDocument).toHaveBeenCalledWith(
+      nestApp,
+      expect.objectContaining(<Omit<OpenAPIObject, 'paths'>>{
+        info: {
+          contact: {},
+          description: documentConfig.description,
+          title: documentConfig.title,
+          version: documentConfig.version,
+        },
+      }),
+    );
+    expect(SwaggerModule.setup).toHaveBeenCalledWith(documentConfig.endpoint, nestApp, swaggerDocument, customConfig);
+  });
+});

src/main.ts

@@ -3,15 +3,15 @@ import { INestApplication } from '@nestjs/common';
 import { DocumentBuilder, SwaggerModule } from '@nestjs/swagger';
 import { AppModule } from './app.module';
 
-async function bootstrap() {
+export async function bootstrap() {
   const app = await NestFactory.create(AppModule);
 
   setupDocument(app);
 
   await app.listen(3000);
 }
 
-async function setupDocument(app: INestApplication) {
+export async function setupDocument(app: INestApplication) {
   const config = new DocumentBuilder()
     .setTitle('Driver License Verification API')
     .setDescription('An unofficial driver license verification crawler API service with live status check support.')