What type of testing focuses on the application's ability to handle requests correctly?

Functional testing is focused on verifying that the application behaves according to specified requirements. It examines the functions of the software application, ensuring that the application responds correctly to a variety of inputs and performs the expected actions. This includes checking whether various features and functionalities work properly and that the application processes input data correctly.

When it comes to handling requests, functional testing scrutinizes whether the application does what it is supposed to do when an end user interacts with it. This involves validating business logic, data manipulation, error prompts, and overall functionality. Essentially, functional testing is about confirming that each feature operates as intended and meets the user's needs, thus confirming the application's ability to handle requests appropriately.

The other testing types serve different purposes. Regression testing checks for new bugs in previously tested functionality after changes were made. Performance testing assesses how well the application performs under various conditions like load and stress. Usability testing evaluates how easy and intuitive the application is to use from the end user's perspective. Each of these types focuses on different aspects of the software, which underscores why functional testing is the right answer in this context.