Levels of Software Testing• Unit Testing• Integration Testing• System Testing• User Acceptance Testing(UAT)Unit Testing• A unit is the smallest testable part of software. It usually has one or a few inputs and usually a single output.• Unit testing conducts on a single program or single module.• Unit Testing is white box testing technique.• Unit testing is conducted by the developers.• Unit testing techniques:• Basis path testing• Control structure testing• Conditional coverage• Loops Coverage• Mutation TestingIntegration Testing• In Integration Testing, individual software modules are integrated logically and tested as a group.• Integration testing focuses on checking data communication amongst these modules.• Integrated Testing is white box testing technique.• Integrated testing is conducted by the developers.• Approaches:• Top Down Approach• Bottom Up Approach• Sandwich Approach(Hybrid)• Stub: Is called by the Module under Test. • Driver: Calls the Module to be tested.Bottom-Up Integration • In the bottom up strategy, each module at lower levels is tested with higher modules until all modules are tested. It takes help of Drivers for testingTop down Integration • In Top to down approach, testing takes place from top to down following the control flow of the software system. • Takes help of stubs for testingSystem Testing • Testing over all functionality of the application with respective client requirements. • It is a black box testing technique. • This testing is conducted by testing team. • Before conducting system testing we should know the requirements. • System Testing focusses on below aspects. • User Interface Testing (GUI) • Functional Testing • Non-Functional Testing • Usability TestingUser Acceptance Testing • After completion of system testing UAT team conducts acceptance testing in two levels. • Alpha testing • Beta testing