Explain Unit testing, Interface Testing and Integration testing. Also explain the types of integration testing in brief?

Unit testing

Unit Testing is done to check whether the individual modules of the source code are working properly. i.e. testing each and every unit of the application separately by the developer in developer's environment.

Interface Testing

Interface Testing is done to check whether the individual modules are communicating properly one among other as per the specifications.
Interface testing is mostly used in testing the user interface of GUI application.

Integration testing

Integration Testing is done to check the connectivity by combining all the individual modules together and test the functionality.

The types of Integration Testing are

1. Big Bang Integration Testing

In Big Bang Integration Testing, the individual modules are not integrated until all the modules are ready. Then they will run to check whether it is performing well.

In this type of testing, some disadvantages might occur like,

Defects can be found at the later stage.It would be difficult to find out whether the defect arouse in Interface or in module.

    2.  Top Down Integration Testing

In Top Down Integration Testing, the high level modules are integrated and tested first. i.e Testing from main module to sub module. In this type of testing, Stubs are used as temporary module if a module is not ready for integration testing.

   3.  Bottom Up Integration Testing

In Bottom Up Integration Testing, the low level modules are integrated and tested first i.e Testing from sub module to main module. Same like Stubs, here drivers are used as a temporary module for integration testing.