Test ARKs should be deleted regularly or else users will get used to them being there and they may become attached to them. The longer an identifier is in place the harder it can be to withdraw it. For example, the EZID system deletes test ARKs older than about two weeks. Duration of any ARK should be discoverable from its persistence statement, which is what the “??” inflection is designed to return.
There are two ways to create test ARKs.
If your organization already has its own NAAN, you can immediately create and use a “quick test ARK”. This is an ARK that starts with ark:/99999/9NNNNN_, where NNNNN represents the NAAN (preceded by ‘9’ and followed by ‘_’). There is no need to register a quick test namespace since it is automatically set aside for each NAAN. As with any prefix, there is an infinite number of possible test ARKs in each NAAN’s quick test namespace. Here are two versions of an example quick test ARK belonging to the BnF (NAAN 12148):
https://ark.bnf.fr/ark:/99999/912148_testxyz
https://n2t.net/ark:/99999/912148_testxyz
Note that N2T.net is configured to forward any quick test ARK it receives (second version above) to the appropriate local resolver (first version).
As mentioned, to implement a shoulder under your own NAAN requires no special request, but the drawback is that recipients have no way of looking at an ARK minted on your test shoulder and knowing that it is a test ARK. But they can tell if the shoulder is under the shared NAAN, 99999, which is well-known for being reserved for testing. So if you need a shoulder under this shared NAAN, and if you want N2T.net to resolve it, you would need to get it listed in the shared NAAN shoulders registry. That means filling out an online shoulder form.