What is Integration Testing?
Integration testing verifies that multiple components work correctly together — testing the interfaces and interactions between modules, services, databases, and external APIs.
Integration testing verifies that multiple components work correctly together — testing the interfaces and interactions between modules, services, databases, and external APIs. Unlike unit tests (isolated) or E2E tests (full system), integration tests focus on the boundaries between components.
Types: Component integration (testing a service with its database), API integration (testing client-server contract), Third-party integration (testing with external APIs using mocks or sandboxes), and Data integration (testing data flows between systems).
Tools: Testcontainers (spin up real databases/services in Docker for tests), Pact (contract testing for APIs), WireMock (HTTP mock server), and database-specific test utilities. Integration tests typically run in CI/CD, not on developer machines.
Why It Matters
Bugs at component boundaries are the most common and the most expensive to fix. Integration tests catch "works in isolation but fails when connected" bugs — the ones unit tests miss.
Frequently Asked Questions
What is integration testing?
Testing that verifies multiple components work correctly together. Focuses on the boundaries: service-to-database, service-to-service, client-to-API. The middle layer of the test pyramid.
Integration test vs E2E test?
Integration tests verify component interactions (service + database). E2E tests verify complete user flows through the entire system. Integration tests are faster and more focused.
Related Terms
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