in itself, an upthrust is usually seen as a confirming indicator of previous weakness.
(apart from times when an upthrust itself is seen on really very high volume, where it would actually be THE climactic or supply bar itself)
So in general, some sort of weakness will be seen (a serious supply event of some type), then an upthrust (or no demand) bar may appear fairly soon after, which can be used to confirm the previously seen weakness (in the supply event).
In this way I guess the upthrust (or no demand) bar can be thought of as a test of demand.....and yes I suppose it is a form of reverse test.