Integration Testing
Testing that verifies different modules or services work correctly together, typically testing interactions between components rather than individual units.
Definition
Integration tests validate that independently developed software modules work together as expected. They sit between unit tests (testing isolated code) and end-to-end tests (testing complete workflows). Common integration test types include: API integration tests, database integration tests, and service-to-service tests. They catch issues that unit tests miss, like incorrect data formats between systems.
Why It Matters
Integration tests catch bugs that appear at component boundaries — the most common source of production issues. While slower than unit tests, they provide confidence that your system works as a whole. A balanced test pyramid includes a significant layer of integration tests.
Example
An integration test verifies that when the UserService creates a user, it correctly calls the EmailService to send a welcome email and stores the user in the database with proper relationships.