E2E testing with supertest in NestJS - Performance & Optimization

Performance: E2E testing with supertest

MEDIUM IMPACT

This affects the speed and resource usage of automated end-to-end tests, impacting test suite run time and developer feedback loops.

Running E2E tests for API endpoints in NestJS using Supertest

NestJS

beforeAll(async () => {
  const moduleRef = await Test.createTestingModule({ imports: [AppModule] }).compile();
  app = moduleRef.createNestApplication();
  await app.init();
});

afterAll(async () => {
  await app.close();
});

test('GET /users returns 200', async () => {
  await request(app.getHttpServer()).get('/users').expect(200);
});

Starting the app once before all tests and closing it after reduces server startup overhead and speeds up the entire test suite.

📈 Performance GainReduces server startups from N times to 1, cutting test suite runtime significantly

Running E2E tests for API endpoints in NestJS using Supertest

NestJS

beforeEach(async () => {
  const moduleRef = await Test.createTestingModule({ imports: [AppModule] }).compile();
  app = moduleRef.createNestApplication();
  await app.init();
});

test('GET /users returns 200', async () => {
  await request(app.getHttpServer()).get('/users').expect(200);
});

Starting a new NestJS app instance before each test causes repeated server startups, increasing total test time and CPU usage.

📉 Performance CostBlocks test execution for multiple seconds per test due to repeated app initialization

Performance Comparison

Pattern	Server Startups	Network Requests	Test Suite Runtime	Verdict
Start app before each test	N times	N requests	High (slow)	[X] Bad
Start app once before all tests	1 time	N requests	Low (fast)	[OK] Good

Rendering Pipeline

E2E tests with Supertest do not affect browser rendering but impact Node.js server startup and network request handling during tests.

→Server Initialization

→Network Request Handling

→Test Execution

⚠️ BottleneckServer Initialization (starting NestJS app instance)

Optimization Tips

1Reuse the NestJS app instance across multiple tests to avoid repeated startups.

2Close the app instance after all tests to free resources.

3Avoid starting the server before each individual test to reduce total runtime.

Performance Quiz - 3 Questions

What is the main performance issue when starting a NestJS app before each E2E test?

A Network requests become slower

B Tests fail due to app state sharing

C Repeated server startups increase total test runtime

D Browser rendering is blocked

DevTools: Node.js Profiler or Jest --runInBand with --detectOpenHandles

How to check: Run tests with profiling enabled or in single-thread mode to measure server startup time and open handles.

What to look for: Look for repeated server initialization logs and long delays before tests start running.