How to Test AWS Services in Node.js with LocalStack, Testcontainers, and Jest

Introduction

Testing AWS-integrated applications presents significant challenges, including slow feedback loops and the cost associated with using cloud resources. In our development workflow, we encountered a critical issue: how to efficiently test AWS services in a local environment without deploying them to the cloud. To address this, we explored a combination of tools that would allow for a local, isolated, and reproducible testing setup.

After thorough research, one of our senior developers identified an optimal solution leveraging LocalStack, Testcontainers, and Jest. This combination enables us to simulate AWS services, manage ephemeral test environments, and execute reliable test cases efficiently. In this article, I will show you how these tools work together and how they can be integrated into a Node.js development workflow for testing AWS-dependent applications.

Overview of Tools

• LocalStack is an open-source tool that provides a fully functional mock environment for AWS services. It allows developers to run their applications locally while simulating AWS services, eliminating the need to connect to a live AWS instance. This significantly reduces cloud costs and improves the speed of development and testing cycles.
• Testcontainers is a library designed to simplify the management of containerized environments for testing. It enables developers to spin up LocalStack instances within isolated containers, ensuring that each test runs in a clean, consistent, and reproducible environment.

Prerequisites

Before proceeding, ensure the following prerequisites are met:

• Node.js and npm are installed on your machine
• Docker is installed and running

Key Considerations

• Testing Framework: This solution is demonstrated using Jest, which will be installed automatically when dependencies are installed via npm. However, other testing frameworks can be substituted based on project requirements.
• Service Compatibility: Verify that LocalStack supports the AWS services required for your tests before integrating it into your testing strategy.

Implementation

To illustrate this approach, I prepared a simple AWS Lambda function that returns a greeting message. The repository also includes a test file (lambda.test.js) to validate the Lambda function’s behavior.

Testing Process

1. Running the test command via npm initializes a local container.
2. The Lambda function’s source code is zipped and deployed inside the container.
3. The test executes the Lambda function and validates the returned response as a standard unit test.
4. All resources are automatically cleaned up upon test completion, ensuring a fast and efficient execution cycle.

Conclusion

By incorporating these tools into our workflow, we have significantly improved test efficiency and resource management. Have you tried using LocalStack or similar tools for AWS testing? We’d love to hear your thoughts and experiences with this approach!