
You’ve been there: Your Unit tests pass both locally and in CI. You deploy with confidence. You thought.. Then staging in the real cloud reveals the truth—bugs that only show up with actual RDS parameter settings, real SQS and SNS throughput limits, or Lambda and API Gateway behaviour your local mocks never captured.
The solution is Testcontainers.
Testcontainers is a testing library that provides easy and lightweight APIs for bootstrapping integration tests with real services wrapped in Docker containers. Using Testcontainers, you can write tests talking to the same type of services you use in production without mocks or in-memory services. Spin them up, run migrations, execute your Node.js service against them, assert results, auto-cleanup.

LocalStack is a cloud service emulator designed for local development and testing of cloud applications. With LocalStack, you can test AWS CloudWatch metric alarms, to get notified on infrastructure failures — all on your local machine! In this video, you will learn how you can use a CloudWatch metric alarm to get notified automatically when your Lambda function invocations fail. You will also set up an email notification using the Simple Email Service (SES) and our Mailhog extension.

Testing in the cloud = slow builds, fragile staging, surprise bills. Let’s talk about how developers are flipping the script and using local cloud environments to test smarter, faster, and cheaper without breaking production. Bonus: You’ll learn how LocalStack lets you simulate AWS on your machine. Game changer.

Why wait for the cloud to test your app? In this episode, we’ll write and run an integration test to validate our LocalStack app. You’ll learn how to upload a file, trigger the Lambda-SQS-DynamoDB flow, and assert the results all locally.