UI (user interface) testing is a methodology that is used on an application's user interface to ensure that it can correctly respond to certain actions, like clicking buttons or filling out forms. It is often used in tandem with unit testing. UIT libraries are used to test C++ applications' UIs. These libraries are a set of classes and methods that support executing a test on an application's UI.
If you're new to C++ UI Testing Open Source libraries then this list will show you how to get started with some of the most popular ones out there today. spix - UI test automation library for QtQuick/QML Apps; Cell - OpenGL C Graphics Engine; Mezz_Test - Testing Tools used in the Mezzanine; SkyUnit - a Testing Framework for Skyrim.