Explain the difference between functional testing and non-functional testing.

Functional testing and non-functional testing are two distinct types of software testing that serve different purposes in ensuring the quality of a software application.

Functional testing focuses on verifying the functional requirements of the software. It aims to ensure that the application behaves as expected and meets the specified functional requirements. This type of testing involves testing individual functions or features of the software to validate if they work correctly and produce the desired output. Functional testing typically includes test cases that cover various scenarios, inputs, and outputs to ensure the software functions as intended.

On the other hand, non-functional testing is concerned with evaluating the non-functional aspects of the software, such as performance, usability, reliability, security, and scalability. Unlike functional testing, non-functional testing does not focus on specific features or functions but rather on the overall behavior and characteristics of the software. It aims to assess how well the software performs under different conditions and whether it meets the non-functional requirements set for it.

Some examples of non-functional testing include performance testing, which measures the software's response time and resource usage under different loads; usability testing, which evaluates the software's user-friendliness and ease of use; security testing, which checks for vulnerabilities and ensures data protection; and reliability testing, which assesses the software's stability and ability to recover from failures.

In summary, the main difference between functional testing and non-functional testing lies in their objectives. Functional testing focuses on verifying the functional requirements and features of the software, while non-functional testing evaluates the software's performance, usability, security, and other non-functional aspects. Both types of testing are essential for ensuring the overall quality and reliability of a software application.