Software Testing: Software Verification & Validation

Both Verification and Validation go parallel with each other. Each verification activity such as requirement specification, functional specification etc. has its corresponding validation activity, such as functional validation, system validation etc. All types of testing methods are performed during validation process. The validation part of the 'Verification and Validation' model comes after verification which involves unit testing, integration testing, system testing, and user acceptance testing.

Terms involved in Validation:

1. Unit Testing
   A unit is the smallest testable part of an application such as methods, classes, interface, and procedure which are tested to determine if they are fit for further use. Unit tests are basically written and executed by software developers to make sure that the written code meets the requirement as specified. Unit testing is performed by 'White Box Testing' method. It is always performed prior to 'Integration Testing'. Unit testing is normally performed by software developers themselves. In rare cases it may also be performed by white box testers. Unit testing helps in simplifying the debugging process.
   
   
2. Integration Testing
   It is a level of software testing where individual units are combined and tested as a group. Purpose of this testing is to find the faults in between the interaction of integrated units. Test drivers and test stubs are used to assist in integration testing. Integration testing is always performed after unit testing and before system testing. Both developers and testers can perform integration testing.
   
   Different approaches of integration testing are as follows:
   
   
   a. Top Down Approach
   In this, the top level units are tested first followed by lower level units. Test stubs are needed to simulate lower level units which may not be available during the initial phase.
   
   b. Bottom Up Approach
   In this, bottom level units are tested first followed by upper level units. Test drivers are needed to simulate high level units which may not be available during the initial phase.
   
   c. Big Bang Approach
   In this, all or most of the units are combined together and tested at one go.
   
   d. Sandwich/Hybrid Approach
   It is a combination of Top-down and Bottom-Up approach.
   
   
3. System Testing
   It is the level of software testing where a complete and integrated software is tested. The main purpose of this testing is to verify that the system to be delivered meets the required specifications. System testing should investigate both functional and non-functional requirements of testing. This testing is performed after Integration testing and before acceptance testing and is normally conducted by a testing team.
   
   
4. Acceptance Testing
   It is a level of software testing where a system is tested for acceptability. It is basically done by the user or customer which mainly focuses on the functionality, thereby validating the fitness for use of the system. This testing is always performed after system testing.

Conclusion

• Both the terms Verification and Validation are essential and balancing to each other.
• Both are used to find a defect in different ways; verification is used to identify the errors in requirement specifications and validation is used to find the defects in the implemented software application.