Quality Assurance (QA) tests look at the functionality of Moodle from a user's point of view.
Real users systematically try each feature in Moodle and test that it works in the current version of the Moodle code.
These tests are repeated in series of cycles, usually just before major releases. Developers and volunteer testers communicate through Tracker on what they find. More information can be found in the Development page also called QA testing.