Testing Levels

Testing levels are:

• Unit Testing
• Integration Testing
• System Testing
• Acceptance Testing

Unit Testing
Testing small testable parts of an application for proper operation is Unit Testing.Usually, unit testing is carried out by Software developers to ensure that the code developed by them meets the specified requirements and behaves as they intended.
Integration Testing
Testing the combined parts of an application to ensure that they function together correctly.
Different types of Integration testing are :

• Bottom-up
• Top-down

Bottom-up integration testing starts with unit testing, and then progress towards higher level combination of units called modules.Dummy modules called 'Drivers' are used for simulation of super-unit.
Top-down integration testing starts with the top integrated modules and then progress towards the smaller units.In this testing,dummy modules called 'stubs' are used to simulate smaller units.
System Testing
Testing based on overall requirements specification and it covers all combined parts of a system.The focus in system testing is typically to ensure that the product responds correctly to all possible input conditions and the product handles exceptions in a controlled and acceptable fashion.
Acceptance Testing
Acceptance testing can mean one of two things:
1.A Smoke test is used as an acceptance test prior to introducing a build to the main testing process.
2.Acceptance testing performed by the customer is known as User Acceptance Testing(UAT).

Before shipping the final version of the software, Alpha and Beta Testing are often done additionally.
Alpha Testing
Simulated or actual operational testing by potential users/customers or an independent test team at the developer's site.
Beta Testing
Beta testing comes after Alpha testing.Versions of the software, known as beta versions are released to a limited audience outside of the programming team.The software is released to groups of people so that further testing can ensure the product has few faults or bugs.