The function qt_register_signal_spy_callbacks will register functions that will be called before / after each signal emission, and before / after each slot call. Although TrollTech does not document this function. it appears that some test utilities use this function. It appears that this function is in a gray area: it is not documented, but it cannot be removed without impacting test software. This makes me wonder: is it safe to use the qt_register_signal_spy_callbacks function? Or should this be regarded as an implementation detail that can go away at any time?