What is "API testing"?

API testing is focused on evaluating application programming interfaces to ensure they function correctly and meet the necessary standards of reliability, performance, and security. This type of testing involves verifying that the APIs return the right responses for various input requests and that they can handle the expected load without failure. It also includes checking for security vulnerabilities, ensuring that only authorized requests can access or manipulate the data exposed by the API.

In the context of quality assurance, API testing is crucial because APIs serve as the backbone for interactions between different software components and services. Functionality tests ensure that APIs perform the tasks they are designed to do, while reliability testing verifies that they can consistently handle requests under different scenarios. Performance testing checks how fast and efficiently the API responds, and security testing assesses the robustness of API security measures against potential threats.

The other options do not capture the essence of API testing. Managing user permissions relates to access control within applications, assessing user experience focuses on the overall interaction and satisfaction with the application, and validating installation procedures pertains to ensuring that software can be properly installed. None of these options encompasses the comprehensive evaluation of APIs that option A does.