Fair enough. It was quite easy to modify NumericDVSorter. Patch adds another ctor which takes a boolean ascending, and integrates it with the test.
This got me thinking if ascending/descending should be on the Sorter.sort API, but I think it shouldn't because someone can dangerously sort some segments in ascending and others in descending order. Better, I think, if it's a consistent decision for all segments. What do you think?