The job of the QA team is just as the name sounds. Assure the quality of the Unreal4.* code. We work directly with the committers of the project to test the code to make sure all features work as expected and all code is stable.
For each bug posted, we attempt to reproduce the bug using any given reproduction steps by the user and mark the bug with our observations. Once the bug is looked at by a developer and a fix is committed, we test the fix to make sure the original issue has been fixed. If this is true, we close the bug and mark it as fixed.