since both animals are "self [aa] all you can get is other self rabbits.
Since the lilac is recessive on aa bb dd you can find out if the tort carries those recessives. That's why a lilac collered rabbit is considered a "test" breeding. It can pair up with hidden recessives and then you know its mate carries those recessive genes.
the black tort is aa B_ C_ D_ ee
if the lilac carries the non-extension "e" then you can get more torts. At least all the kits will be non-extension carriers.
The most likely kits will be black, both solid and broken.
If the tort carries dilute "Dd" you can also get blue, solid and broken.
if the tort carries brown "Bb" you can get chocolate, solid and broken.
and if the tort carried BOTH brown and dilute you can get lilac, both solid and broken.
If the tort & the lilac carry albino "Cc" then it's also possible to get REW.
There are other recessives that could be hidden on the C locus but I figure these are enough options for now