Testing
Unit tests with mocked AWS SDK calls tell you that your function logic is correct. They don't tell you whether your DynamoDB queries actually work, whether your S3 key paths are right, or whether your SQS message format triggers the right Lambda. LocalStack fills that gap: it runs
Testing
AWS SQS and SNS are everywhere in serverless and microservice architectures. They're also surprisingly easy to test badly.
Testing
moto is great for unit tests but stops at service boundaries. When you need SQS triggering Lambda, SNS fan-out to multiple SQS queues, or Lambda updating DynamoDB — you need LocalStack. This guide sets up a full LocalStack integration test environment with Docker Compose, pytest fixtures, and reusable infrastructure helpers.