Testing Microservices and Distributed Systems
Microservices and distributed systems present testing challenges that monolithic applications do not: network failures, eventual consistency, service interdependencies, and emergent behaviour from service interactions. A testing strategy for distributed systems must address each of these specifically.
Service-Level Testing
Each microservice should have its own comprehensive test suite: unit tests for business logic, integration tests for its own database/cache interactions, and API tests for its exposed interfaces. Services should be testable in isolation — with downstream dependencies mocked or stubbed.
Contract Testing
Contract testing (Pact) verifies that service interfaces are compatible without requiring all services to be running simultaneously. Consumer-driven contracts define what each service expects from its dependencies. Provider services verify they satisfy all consumer contracts. This enables independent deployment of services with confidence that integration won't break.
Integration Testing in Distributed Systems
Full integration testing of all services simultaneously is expensive and fragile. Use a test double strategy: test services against stubs that simulate their dependencies, supplemented by targeted integration tests of critical inter-service interactions. Reserve full-stack integration tests for critical system-level journeys.
Chaos Engineering
Chaos engineering systematically introduces failures — stopping services, introducing network latency, exhausting resources — to verify that the system degrades gracefully and recovers correctly. Netflix's Chaos Monkey pioneered this approach. Valuable for validating resilience assumptions in production-like environments.