Improving XRootD's testing suite

This document presents a comprehensive exploration of the enhancements made to the testing methodologies within the XRootD project. We explore the transition from legacy testing frameworks like CppUnit to modern alternatives, particularly GoogleTest, as well as the introduction of a local test data generation and the optimization of testing processes by replacing a container-based approach with one based on local instances of XRootD. The result is not only a significant increase in code coverage but also a reduction in testing time. Tests now run seamlessly within the CI pipeline with every commit. We conclude by addressing future opportunities, emphasizing the potential for further code coverage expansion through the additions of tests related to authorization methods and Zip archives.