What is a key focus of functional testing?

Functional testing primarily focuses on verifying that the software system operates according to specified requirements. It assesses the functions of the application against the defined specifications, ensuring that each feature behaves as expected. While interoperability of components is an important aspect, functional testing is more concerned with whether the individual functions of the system fulfill the user's needs.

The emphasis on functional testing involves checking the correctness of the functionality, including input processing, output generation, and error handling, based on various test cases. This means that the tests validate the interactions and responses of the system's components but not specifically how those components interact across different systems or platforms, which would typically fall under the scope of integration testing.

Other options touch on important aspects of software quality assurance, but they do not align with the primary objectives of functional testing. For instance, system performance under stress is a focus of performance testing, analyzing internal code structure relates to static code analysis or structural testing, and checking for user accessibility involves evaluating accessibility standards, which are critical for end-user experience but are not the core emphasis of functional testing itself.