... is there a standard way to proceed?
Not really, at least as far as I know. Both sfo2's answer and onnoweb's answer have good points: On one hand, if you're ready for the test now, you should do well and then don't have to keep studying just to stay current (or don't have to cram later) and you may have a leg up on other candidates later; on the other hand, the position may never open up, and if it does the requirements may change.
More information is what is needed here. Some things you might want to ask before making a decision: Why was the position put on hold? How long will it be on hold? (As alluded to above) Will the requirements change? You might not get firm (or even honest) answers, but if the job was placed on hold because the supervisor just resigned, it tells you something different than if the budget got cut.
Another factor: are you ready for the test now? If not, a delay to study up might help. You just have to be sure to keep studying until you can take the test.
Finally: Is this a test that will cost you somehow? Not just the possibility that you might have to pay for it, but would you have to take a vacation day (or leave without pay) from your current job, or maybe have to travel to the testing site? For me, taking the test in the evening while at home and wearing my pajamas is a lot more enticing that taking a day off, maybe getting dressed up, and driving out of my way to take a test for a job I might get considered for ... someday.