Definition
Integration testing is a level of software testing where individual software modules or components are combined and tested as a group. The purpose is to expose faults in the interaction between integrated components, focusing on the interfaces and data flow between modules.
Types of Integration Testing
Big Bang Integration
All components are integrated simultaneously and tested as a whole system.
- Pros: Simple approach, less planning required
- Cons: Difficult to isolate faults, debugging is complex
Incremental Integration
Components are integrated one by one and tested at each step.
Top-Down Integration
Integration starts from top-level modules and proceeds downward.
- Uses test doubles (stubs) for lower-level modules not yet integrated
- Allows early testing of major control and decision points
Bottom-Up Integration
Integration starts from lowest-level modules and proceeds upward.
- Uses test drivers to simulate higher-level modules
- Allows early testing of utility and foundational components
What Integration Tests Verify
- Data transfer: Correct data exchange between components
- Interface contracts: APIs and method signatures work as expected
- Error handling: Proper propagation and handling of errors across boundaries
- Performance: System behavior under realistic load conditions
- Configuration: Components work together with shared configuration
Common Integration Scenarios
- Database integration: Application logic with data persistence layer
- API integration: Frontend applications with backend services
- Third-party services: Integration with external APIs or services
- Microservices: Communication between distributed services
Best Practices
- Start integration testing early in development cycle
- Use realistic test data that represents production scenarios
- Test both happy path and error conditions
- Maintain separate test environments that mirror production
- Focus on critical business workflows first