Design and Implement Microservice Integration Tests

Designs, implements, and maintains integration tests for microservice architectures - covering the test pyramid for distributed systems, containerized test environments, contract testing, event-driven flow validation, failure scenario testing, and load testing.

Use this skill when building an integration test suite for services that communicate over APIs or events, writing contract tests between a consumer and provider service, testing distributed transaction consistency across services, validating circuit breaker and timeout behavior, or load testing a service and its downstream dependencies together. Not a fit for pure unit testing of a single service in isolation or for UI/end-to-end browser testing.

Defines a four-layer test pyramid for microservices: contract tests (API contracts via tools like Pact), component tests (isolated services with mocked dependencies), integration tests (service interactions with real dependencies), and end-to-end tests (minimal, critical user journeys only). Testing strategy starts with mapping service dependency graphs and distinguishing synchronous from asynchronous communication patterns.

Provides a Docker Compose test environment definition wiring multiple services (user-service, order-service) to their databases, cache, and each other via environment variables, plus a TestDataManager class for setting up and tearing down test users, products, and cache state between test runs.

Shows a Pact-based contract test verifying a consumer (order-service) against a provider (user-service) API interaction, an event-driven integration test that subscribes to multiple event types (user.validated, inventory.reserved, order.created) and validates each event's payload after triggering an order flow, and resilience tests validating a 5-second timeout with fallback response and circuit-breaker-open behavior after repeated failures (asserting fast-fail under 100ms).

Database integration testing covers a distributed transaction test verifying user balance and inventory are both updated correctly on a successful order, and a rollback test confirming no state changes occur when an order fails due to insufficient funds. Load testing uses autocannon to drive concurrent requests against an endpoint while monitoring downstream service health, asserting error rate and average response time thresholds.

Best practices cover organizing tests by service boundary, test isolation with cleanup between runs, including distributed tracing and log capture during test execution, running contract tests on every build vs. full integration tests in staging, and common pitfalls like testing every service combination or relying on external services for critical tests.

Uses Docker Compose for test environment orchestration, Pact for contract testing, autocannon for load testing, and JavaScript/Jest-style test patterns throughout, with PostgreSQL and Redis as example backing services.

Backend and platform engineers building or hardening an integration test suite for a microservice system who need concrete contract, event, resilience, and load test patterns rather than a general testing philosophy.

const provider = new Pact({
  consumer: 'order-service',
  provider: 'user-service'
});