In http://en.wikipedia.org/wiki/Computer_programming - computer programming , unit testing is a procedure used to validate that individual http://en.wikipedia.org/wiki/Module_%28programming%29 - modules or units of http://en.wikipedia.org/wiki/Source_code - source code are working properly.

More technically one should consider that a unit is the smallest testable part of an application. In a Procedural Design a unit may be an individual program, function, procedure, web page, menu etc. But in Object Oriented Design, the smallest unit is always a Class; which may be a base/super class, abstract class or derived/child class.

A unit test is a test for a specific unit. Ideally, each http://en.wikipedia.org/wiki/Test_case - test case is independent from the others; http://en.wikipedia.org/wiki/Mock_object - mock objects and http://en.wikipedia.org/wiki/Test_harness - test harnesses can be used to assist testing a module in isolation. Unit testing is typically done by the http://en.wikipedia.org/wiki/Software_developer - developers and not by http://en.wikipedia.org/wiki/End-user - end-users .