Unit testing is the testing process in software testing to verify that the smallest testable part or a unit of an application, are tested independently and individually to verify that specific unit is working fine as per requirement or not.
Generally software developers have to do Unit testing when they develop smallest part of an application. After development of specific unit of an application, developer check and verify that how behaves new developed unit independently. If there is any error or bug then they have to solve it in first stage.
Here is the simple example of Unit testing
Suppose there is developed one functionality for add, edit and delete records. Now when user clicks on edit button, it proceeds for deleting the record. Then it is not right operation. It is called bug in IT industry. This mistake is done by developer during the unit's development of an application. This bug should be solved before the integration of two or multiple Units of application.
Why unittest Require?
There is one fact in software industry is bugs found during early testing phase are less cost and time consuming than bugs found during latter stage. In software testing life cycle, Unit test is the first stage means early stage than the other testing phases. So if Unit testing is done and bugs founded and fixed during unittest phase are less time and cost consuming.
One more thing if unit test is not done and if that unit is integrated with any another unit then integration testing is not possible. Because for integration testing specific units should must work properly. That’s why unittest is compulsory for integration testing.