Which type of testing is essential before finalizing a software application upgrade?

Regression testing is essential before finalizing a software application upgrade because it helps ensure that recent code changes or enhancements have not adversely affected the existing functionality of the application. When an upgrade is implemented, new features or improvements may be introduced, and regression testing assesses the entire application to confirm that previously working features remain intact and perform as expected.

This type of testing involves running a suite of tests that covers the core functionalities of the application to catch any unintended side effects of the upgrade. It is crucial for maintaining software quality and reliability, particularly when multiple changes occur simultaneously, as it provides a safety net against introducing new bugs or issues.

While acceptance testing examines whether the software meets business requirements, unit testing focuses on individual components, and performance testing evaluates the system's responsiveness and stability under load, regression testing specifically addresses the risks associated with changes made during an upgrade.