Integration testing

Integration testing checks that separate parts of a system work correctly together, such as a service and its database, two microservices, or an app and a third-party API. It sits between unit tests, which test one piece in isolation, and end-to-end tests, which test a whole user journey.

What integration tests catch

• Wrong data formats or field names between services.
• Database queries, migrations and transactions that fail with real data.
• Authentication, timeouts and error handling between components.

Common approaches

• API-level tests that call a service and check its response and side effects. See API testing.
• Contract tests that check two services agree on the shape of their messages.
• Containerised dependencies, such as a real database started in Docker for each test run.

Keep integration tests fewer than unit tests but more than end-to-end tests, as the test pyramid suggests.

Read the full guide: Best API Testing Tools 2026 — Honest Reviews for QA Engineers