What is integration testing?
Integration testing verifies that separate components, services or systems work correctly together.
Units that work alone can still fail together: a service sends a date in the wrong format, a queue consumer expects a field that is no longer sent, a database migration changes a type. Integration tests exercise those boundaries directly.
They sit between unit tests and end-to-end tests. They are faster and more focused than full journeys but test real interactions rather than mocks.
Example
An integration test sends an order from the checkout service to the fulfilment service through the real message queue and checks the fulfilment record is created with the right items.
Best practices
- Test each boundary between services or systems
- Use real dependencies or high-fidelity test doubles
- Include failure cases such as timeouts and malformed messages
- Run in CI on every change to either side
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