To answer this question, you need to understand different testing techniques. Let's go through each option to understand why it is correct or incorrect:
Option A) Black-box testing - This option is correct because black-box testing is a testing technique that focuses on testing the functionality of a program without considering its internal structure or implementation details. Test cases are devised to demonstrate that each program function is operational, without knowledge of the internal code.
Option B) Glass-box testing - This option is incorrect because glass-box testing, also known as white-box testing, involves testing the internal structure and implementation of a program. It requires knowledge of the internal code and is not focused on demonstrating the operational functionality of each program function.
Option C) Grey-box testing - This option is incorrect because grey-box testing is a combination of black-box and white-box testing techniques. It involves having partial knowledge of the internal code and using that knowledge to design test cases. Grey-box testing does not necessarily focus on demonstrating the operational functionality of each program function.
Option D) White-box testing - This option is incorrect because white-box testing, also known as glass-box testing, involves testing the internal structure and implementation of a program. It requires knowledge of the internal code and is not focused on demonstrating the operational functionality of each program function.
The correct answer is A) Black-box testing. This option is correct because black-box testing is the testing technique that requires devising test cases to demonstrate that each program function is operational, without considering the internal structure or implementation details of the program.