We've never tested.
We are undoubtedly in the minority, but our DD13 is clearly EG, probably PG (she's acing AP Lit and admitted that this is one of her "fun" classes that "isn't that hard"), and we've been able to let her ability speak for itself rather than focusing on a number derived from independent testing.
Our reasons may sound odd, but we felt that testing was focusing on WHAT our child is instead of WHO she is, and we definitely didn't want the school doing that if it wasn't needed.
No good could come of it in our opinion and individual circumstances; either she tests LOWER than her function would indicate, in which case, lots of "WTH??" kinds of questions and a microscope to figure out why she isn't "testing" better... is it a disability? What kind?? (well, in one respect, she seems to be awfully functional in spite of that, so again, what's to be gained if she's using compensatory strategies so effectively that she's for all intents and purposes "unimpaired?")
Or-- the number is HIGHER than we think. (Possible.) Still, if it's THAT high, then we risk anyone who sees it turning her into a caricature/circus side show rather than treating her as an individual that they know. I experienced some of this, and it can be very damaging with adults who don't understand that you aren't just a guinea pig or specimen. Scores over 165 are REALLY out there for most educators, and she already knows (from daily experience) that her experiences of the world differ qualitatively from many peers, even gifted peers. She's only met a couple of peers who were at similar LOG.
So we're comfortable with "probably mid 150's to mid 160's, maybe higher."
If there were particular nagging problems, we'd definitely seek out formal evaluation. There are some times when we've wished fleetingly that we HAD the numbers. It just hasn't been necessary. We've had a school system that has listened well to me as an advocate, has proven to be reasonably flexible about placement options, and we've been willing to do some pretty radical things ourselves in terms of educational accommodation.
Partly, we've learned to be wary of testing for its own sake-- we've been down that rabbit hole a time or two with medical stuff, and there does come a point where the numbers don't TELL you anything of functional significance, and you wind up with MORE questions instead of answers.
Bottom line? What information do you think that you would get that you don't already have? What would you DO with the information?