Probably not, but it's always nice to follow intended designs, since others will do so as well and this allows systems to evolve in compatible ways. There may be no difference today, but there could be tomorrow.

These days invalid TLDs don't really exist. New ones are getting released all the time. The only problem you'd run into is if the system you're using is treating .test differently for some reason, but that's likely not the case, for obscurity reasons if nothing else.