Integration Testing is a phase in software testing where individual units or components of a software application are combined and tested as a group. The primary goal of integration testing is to identify issues that arise when different modules or services interact with each other. This type of testing is crucial in ensuring that the interfaces between components work correctly, that data is passed between them as expected, and that the integrated system meets the specified requirements. Integration testing typically follows unit testing, where individual components are tested in isolation, and precedes system testing, where the complete application is tested.

There are several approaches to integration testing, including top-down, bottom-up, and big bang testing. In top-down integration testing, higher-level modules are tested first, with lower-level modules added incrementally. In bottom-up testing, lower-level modules are tested first and then integrated with higher-level modules. Big bang testing involves integrating all modules at once and testing them together. Each approach has its advantages and challenges, depending on the complexity of the system and the dependencies between components. Effective integration testing helps to ensure that the final software product is robust, reliable, and free of critical integration issues.