[blueblimp]

It's untested in the sense that no genetic engineering has been done in humans, yes. (Unless you count gene therapy to cure disease, which is fairly different.)

However, there are some pretty strong reasons to think it would work, at least if we're just talking about improving within the typical range of human ability. Going to the extremes of existing ability and beyond is probably possible too, but there are more unexpected problems that could exist.

[the8472]

Has IQ-improving gene-editing been proven in animals then?

[blueblimp]

Yes: http://www.sciencemag.org/news/2014/09/human-speech-gene-can.... (That said, you'd need to use a different approach in humans, because we don't have any smarter species that we can copy genes from.)