What is Integration Testing

Definition

Integration testing verifies that separately developed components or services work correctly when combined, checking the interactions, data flow, and interfaces between them to catch defects that only appear when units are wired together.

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Catches defects in how components interact that unit tests cannot see
Validates interfaces, data flow, and contracts between modules
Reduces surprises when integrated parts meet in production
Builds confidence that combined components behave as a whole

Real World Example

After unit-testing a payment module and an order module separately, the team runs integration tests confirming that placing an order correctly triggers and records a payment across the two services.

FAQs

What does integration testing check?

It checks that combined components work together correctly, focusing on their interfaces, interactions, and data flow.

How is it different from unit testing?

Unit testing isolates single components, while integration testing exercises multiple components working together.

What problems does integration testing catch?

Interface mismatches, incorrect data exchange, and faulty assumptions between components that only surface when they interact.