What is unit testing?

The main objective of Unit testing is to test each and every function.Generally unit test is done by developer.It is conducted before integression testing.

A small piece of testable program is tested under Unit Testing Phase.

The application is divided into different modules as units and testing is performed on each single module. Developers basically perform it. 
 

Unit Testing is the testing the application when the application is in the development stage where the developers concentrate on developing the application as small unit programs, later all these units/objects/components are integrated to make a complete application. The testing performed on this units of programs are called unit testing. Usually, developers who are developing that particular part will be tested to make sure that his portion of the code is according to the specifications. The developer prepares some raw input and output conditions for testing his development work. This data is useful for the testers as well to prepare the efficient test cases.

A set of one or more computer program, a source code that aims to test unit of program, its a sort of white box testing techniques implemented by developer for an early defect detecting and also to facilitate integration