What is integration testing?

'Integration testing' refers to a software development activity.

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.

Integration testing takes as its input modules that have been checked out by unit testing, groups them in larger aggregates, applies tests defined in an Integration test plan to those aggregates, and delivers as its output the integrated system ready for system testing.

Most large projects have a lot of parts, each being individually developed by a separate team.
Each part while being individually developed, goes through atleast two types of testing
- unit testing : where that particular unit is tested in isolation, assuming that it is given different kinds of simulated inputs and how it fares with them
- integration testing: all the modules have been developed by now. they get jointly compiled and integrated. The same is now tested against real/simulated data. This phase is called integration testing