Testing AWS integrations against real AWS services requires IAM credentials, costs money per test run, and creates real side effects (files in S3, messages in SQS). LocalStack runs a local AWS cloud emulator in Docker — the same API, the same response format, but running locally with no AWS account required. This article covers testing S3, SQS, and SNS integrations with LocalStackContainer. What You’ll Learn LocalStackContainer setup and @ServiceConnection Creating S3 buckets and testing file upload/download Testing SQS message producers and @SqsListener consumers Testing SNS to SQS subscriptions Creating AWS resources before tests with the AWS SDK Testing DynamoDB operations Dependencies <dependency> <groupId>io.