What is Integration Testing

Integration testing (sometimes called Integration and testing and abbreviated I&T) is the phase of software testing in which individual software modules are combined and tested as a group. It follows unit testing and precedes system testing.

The purpose of Integration testing is to verify functional, performance and reliability requirements placed on major design items. These “design items”, i.e. assemblages (or groups of units), are exercised through their interfaces using Black box testing, success and error cases being simulated via appropriate parameter and data inputs.
The overall idea is a “building block” approach, in which verified assemblages are added to a verified base which is then used to support the Integration testing of further assemblages.
The different types of integration testing are Big Bang, Top Down, Bottom Up, and Back bone.