What is Integration Testing
It is the second level of testing after unit testing.In this level of software testing individual units are combined and tested as a group. The purpose of this level of testing is to find bugs in the interaction between integrated units.
Need of Integration Testing
Different modules are developed by different developers so it become necessary to test the all units after integration .In most of the applications it interacts with some third party tools or APIs which also need to be tested
•Now in Agile era requirements changes frequently many a time developer deploys the changes without unit testing it. Integration testing becomes important to minimize the chances of integration issues.
•Test drivers and test stubs are used in Integration Testing as simulators if required.
Approaches of Integration Testing
Big Bang Approach-
Big bang approach integrates all the modules at once It verifies if the system works as expected or not after integration. If any issue is detected in the completely integrated module, then it becomes difficult to find out which module has caused the issue.
Bottom -Up Approach
Bottom-up testing starts from the lowest unit of the application, and gradually moves up.This integration continues till all the modules are integrated and the entire application is tested as a single unit.If the upper module is not developed then simulator is used which is called driver
Top Down is an approach to Integration Testing where top-level units are tested first and lower level units are tested after that.If the lower module is not developed then simulator is used which is called Stub.