What is Integration Testing (I&T)?


Integration testing, also known as integration and testing (I&T), is a software development process which program units are combined and tested as groups in multiple ways. In this context, a unit is defined as the smallest testable part of an application. Integration testing can expose problems with the interfaces among program components before trouble occurs in real-world program execution. Integration testing is a component of Extreme Programming (XP), a pragmatic method of software development that takes a meticulous approach to building a product by means of continual testing and revision.

There are two major ways of carrying out an integration test, called the bottom-up method and the top-down method. Bottom-up integration testing begins with unit testing, followed by tests of of progressively higher-level combinations of units called modules or builds. In top-down integration testing, the highest-level modules are tested first and progressively lower-level modules are tested after that.

In a comprehensive software development environment, bottom-up testing is usually done first, followed by top-down testing. The process concludes with multiple tests of the complete application, preferably in scenarios designed to mimic those it will encounter in customers’ computers, systems and networks.

Types of integration testing
To explore how integration testing is used in the enterprise, here are some additional resources for learning about testing:
How to do integration testing: The top-down and bottom-up approaches for integration testing are both critical. Expert John Overbaugh explains the differences between them and the reasons for their importance.
Functional testing: Unit testing, integration testing and beyond: Integration tests and unit tests both test the functionality of software, but they alone cannot replace functional testing. Expert Karen N. Johnson explains how integration and unit tests work and offers ideas for other functional tests.

This was last updated in March 2008

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