A new navigation system compared with a previous system is the most suitable application for testing by use cases, because it involves a high level of interaction between the user and the system, and the expected behavior and outcomes of the system are based on the user’s needs and goals. Use cases can help to specify the functional requirements of the new navigation system, such as the ability to enter a destination, select a route, follow the directions, receive alerts, etc. Use cases can also help to compare the accuracy and usability of the new system with the previous system, by defining the success and failure scenarios, the preconditions and postconditions, and the alternative flows of each use case. Use cases can also help to design and execute test cases that cover the main and exceptional paths of each use case, and to verify the satisfaction of the user’s expectations.

The other options are not the most suitable applications for testing by use cases, because they do not involve a high level of interaction between the user and the system, or the expected behavior and outcomes of the system are not based on the user’s needs and goals. A billing system used to calculate monthly charge based on a large number of subscriber parameters is more suitable for testing by data-driven testing, which is a technique for testing the functionality and performance of a system or component by using a large set of input and output data. The ability of an antivirus package to detect and quarantine a new threat is more suitable for testing by exploratory testing, which is a technique for testing the functionality and security of a system or component by using an informal and flexible approach, based on the tester’s experience and intuition. The suitability and performance of a multimedia (audio video based) system to a new operating system is more suitable for testing by compatibility testing, which is a technique for testing the functionality and performance of a system or component by using different hardware, software, or network environments. References = CTFL 4.0 Syllabus, Section 3.1.1, page 28-29; Section 4.1.1, page 44-45; Section 4.2.1, page 47-48.