To answer this question, you need to understand the concept of functional and non-functional testing methods.
Functional testing refers to testing the functionality of a system or software application, ensuring that it meets the specified requirements. On the other hand, non-functional testing focuses on testing the system's non-functional aspects, such as performance, usability, security, reliability, and scalability.
Let's go through each option to understand why it is correct or incorrect:
Option A) System testing - System testing primarily focuses on testing the functionality of a system. It is a type of functional testing and does not fall under non-functional testing. Therefore, this option is incorrect.
Option B) Usability testing - Usability testing evaluates how user-friendly and intuitive a system or software application is. It falls under the category of non-functional testing as it assesses the system's usability, which is a non-functional aspect. Therefore, this option is correct.
Option C) Performance testing - Performance testing is conducted to evaluate the system's performance under specific conditions, such as load, stress, and volume. It also falls under the category of non-functional testing as it focuses on the system's performance, which is a non-functional aspect. Therefore, this option is correct.
Option D) Both b & c - Option D states that both usability testing and performance testing are non-functional testing methods. Based on the explanations provided above, this option is correct.
The correct answer is D) Both b & c. This option is correct because usability testing and performance testing are both non-functional testing methods that assess the non-functional aspects of a system or software application.