Well, even if you have a necessity test, you still need to decide, on a factual basis, whether this particular information is necessary to achieve that particular program. The answer is not always obvious. Reasonable people might disagree about what is necessary to be collected for a particular purpose.
Putting a necessity test in the act itself does not make that issue disappear on its own. There will always be some discussion about what is exactly necessary to collect in terms of personal information for a particular program.