D has documented unittests (they appear in the docs as if part of the Examples section). The only excuses for example code in Phobos to be untested are supposed to be that it is an incomplete fragment or that it is old code from before we had the feature.— David
I added some just recently, because it wasn't possible to add unittest to the module level.
https://github.com/D-Programming-Language/phobos/blob/master/std/container/package.d
