Testing
Dead letter queues (DLQs) are the safety net of event-driven systems. When a message can't be processed after N retries, it goes to the DLQ for manual inspection or alternative processing. Most teams test the happy path but skip testing DLQ behavior — which means they discover bugs
Testing
RabbitMQ integration tests need a real broker to catch routing failures, binding misconfiguration, and dead-letter queue behavior that mocks will never surface. This guide covers testing exchanges, queues, bindings, and DLQs with Testcontainers — for both local development and CI pipelines. Key Takeaways Test the routing topology, not just message
Testing
HTTP contract testing is well understood. You define the request and response, Pact records them as a contract, and the provider verifies it. But microservices don't only communicate over HTTP — they publish and consume events through Kafka topics, SQS queues, and SNS topics. Those async channels need contracts
Testing
Testing message ordering and exactly-once delivery in event-driven systems is one of the hardest testing problems in distributed systems engineering.
Testing
Testing asynchronous, event-driven systems is genuinely hard. The problems stack up fast: you can't assert response.status_code == 200 when the operation happens asynchronously; your test needs to know when to stop waiting; race conditions create flaky tests that pass locally and fail in CI; and the
Testing
Kafka Streams provides a TopologyTestDriver that runs your entire stream processing topology in-process — no Kafka cluster needed. You pipe records in through TestInputTopic, read results from TestOutputTopic, and advance wall-clock time programmatically to test windowed aggregations. For Schema Registry integration, use MockSchemaRegistryClient to avoid hitting a real registry.
Testing
RabbitMQ, NATS, and Kafka have dramatically different testing developer experiences. NATS wins on speed and simplicity with its embedded server. RabbitMQ is straightforward with Testcontainers. Kafka requires the most setup but has the richest ecosystem for testing. This comparison helps you understand what you're signing up for before
Testing
Event-driven architectures are notoriously difficult to test. The fundamental challenge: your service publishes an event and returns immediately.