Summary
Integration testing sits between unit testing and end-to-end testing in the test pyramid, validating the interactions between components such as databases, APIs, message queues, and microservices.
What is Integration Testing?
While unit tests verify individual functions in isolation, integration tests confirm that those functions work correctly when combined with real or near-real dependencies. A typical integration test might start a database container, insert data, invoke application code, and assert the result persists correctly.
Integration tests are slower than unit tests but faster and more targeted than full end-to-end tests. They catch problems that only emerge at boundaries: serialization mismatches, transaction handling, network timeouts, or misconfigured service clients.
Tools like Testcontainers allow integration tests to spin up real database or messaging infrastructure in Docker, keeping tests reproducible without requiring a shared environment.
Why is Integration Testing relevant?
- Boundary validation: Catches bugs in the interactions between components that unit tests cannot detect
- Confidence without full E2E cost: Provides high confidence in component integration at a fraction of end-to-end test maintenance effort
- Microservices suitability: Essential for verifying contracts between services in distributed architectures