Integration Testing
Testing that verifies two or more components or services work correctly when combined, focusing on the interfaces and data flow between them.
Integration testing sits between unit testing and end-to-end testing in scope. Where unit tests verify individual functions in isolation and E2E tests cover full workflows, integration tests check that connected modules communicate correctly. For web applications, common integration test targets include API endpoints, database queries, authentication flows, and third-party service interactions.
Why It Matters for QA Teams
Most website bugs occur at the boundaries between systems, such as a front end misinterpreting an API response or a payment gateway returning an unexpected status code. Integration tests target exactly these failure points.
Example
An integration test sends a POST request to the /api/subscribe endpoint with a valid email address and verifies that: the API returns a 201 status, the subscriber record appears in the database, and the email service receives a confirmation trigger. No browser is involved; the test exercises the back-end integration directly.