To answer this question, we need to understand what functional testing is and where it can be performed.
Functional testing is a type of testing that focuses on testing the functionality of a software application. It involves testing the individual functions or features of the application to ensure that they work correctly and meet the specified requirements.
Functional testing can be performed at different levels of testing, including:
A. At system and acceptance testing levels only - This option is incorrect. Functional testing is not limited to just the system and acceptance testing levels. It can be performed at other levels as well.
B. At all test levels - This option is correct. Functional testing can be performed at all test levels, including unit testing, integration testing, system testing, and acceptance testing. This allows for comprehensive testing of the software application's functionality throughout the development lifecycle.
C. At all levels above integration testing - This option is incorrect. Functional testing can be performed at the integration testing level and all levels above it, including system testing and acceptance testing.
D. At the acceptance testing level only - This option is incorrect. Functional testing is not limited to just the acceptance testing level. It can be performed at other levels as well.
The correct answer is B. Functional testing can be performed at all test levels to ensure that the functionality of the software application is thoroughly tested.