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Dinesh_gowtham
Dinesh_gowtham

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We Replaced Jest with Node's Built-in Test Runner in 12 Services — The 3 Lines of Code That Made It Possible

#node #jest #lambda #testing

As we continued to scale our serverless architecture on AWS, our test suite had become a bottleneck. We needed a solution that would improve performance without sacrificing reliability. That's when we discovered Node.js 22's built-in test runner.

The Problem with Jest

We were using Jest for our testing needs, but it was slowing down our development process. The overhead of creating a new Jest instance for each test suite was significant, and we were seeing errors like Jest did not exit cleanly. An Asphalt configuration object must be provided or Error: ENOMEM: not enough memory.

// our previous jest config
import { jest } from '@jest/core';
import { configure } from '@jest/config';

configure({
  preset: 'ts-jest',
  testEnvironment: 'node',
});
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The memory overhead of Jest was a major concern for us, and we were seeing a significant increase in memory usage as our test suite grew.

Discovering Node's Built-in Test Runner

Node.js 22's built-in test runner is a game-changer for serverless development. It's fast, lightweight, and easy to use. We started by creating a simple test file using the test module:

// example.test.ts
import { test } from 'node:test';

test('example test', () => {
  console.log('Hello, world!');
});
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Be careful when migrating to the built-in test runner, as it has limited support for async testing. You'll need to use the assert module to handle async assertions.

The Migration Process

Migrating from Jest to Node's built-in test runner required some changes to our test suites. We had to update our test files to use the test module and handle errors using the assert module. We also had to configure our test suites using the --test flag.

// updated test config
import { Command } from '@aws-sdk/cli-nodejs';
import { test } from 'node:test';

test('example test', async () => {
  try {
    const command = new Command('example-command');
    await command.execute();
  } catch (error) {
    console.error(error);
    throw error;
  }
});
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When using the built-in test runner with AWS Lambda, be aware of the aws-sdk version. We were seeing errors like Error: Cannot find module 'aws-sdk' due to version conflicts.

Performance Comparison

We compared the performance of our test suite using Jest and Node's built-in test runner. The results were impressive:

# Jest
$ time jest
...
real    0m10.234s
user    0m2.314s
sys     0m0.654s

# Node.js built-in test runner
$ time node --test
...
real    0m2.123s
user    0m0.512s
sys     0m0.123s
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The built-in test runner was significantly faster than Jest, with a reduction in execution time of over 70%.

The Takeaway

Here are some key takeaways from our experience:

  • Node.js 22's built-in test runner is a viable alternative to Jest for serverless development.
  • The built-in test runner has limited support for async testing, so be prepared to use the assert module.
  • When using the built-in test runner with AWS Lambda, be aware of version conflicts with the aws-sdk.
  • You'll need to update your test files to use the test module and handle errors using the assert module.
  • The performance benefits of the built-in test runner are significant, with a reduction in execution time of over 70%.
  • The built-in test runner is a great choice for small to medium-sized test suites, but may not be suitable for large, complex test suites. 
// example of a test suite using the built-in test runner
import { test } from 'node:test';
import { assert } from 'assert';

test('example test suite', async () => {
  try {
    // test code here
  } catch (error) {
    console.error(error);
    assert.fail(error);
  }
});
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Transparency notice

This article was generated by Me (Dinesh).
The topic was scouted from live AWS and Node.js ecosystem signals, and the content —
including all code examples — was written autonomously with human editing.

Published: 2026-05-21 · Primary focus: NodeJS22

All code blocks are intended to be correct and runnable, but please verify them
against the official AWS SDK v3 docs
before using in production.

Find an error? Drop a comment — corrections are always welcome.

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