What is Unit Testing ? Level of Testing :
1 . Unit Testing : It also known as components, module or program testing. It is done by developers before the setup is handed over to the testing team to formally execute the test cases. It is performed by the developers on the individual units of source code assigned areas. The developers use test data that is different from the test data of the quality assurance team. Most often stubs and drivers are used to replace the missing software and simulate the interface between the software components. 
This Testing done before Integration testing