That's not totally true. Very often the congress will authorize pilot studies or regulatory agencies will grant waivers to run experiments. Additionally, congress will put in sunset clauses into laws so that they must be reviewed periodically or automatically expire.
However, these tools are not necessarily used consistently at any level of government....
take the case for usa freedom act or patriot act or any law that snoopers cite in their support. i've never seen any pilot studies on them whatsoever. please dont cite private studies or studies conducted by snoopers themselves. all laws needed to be tested, not just some or atleast when its abused massively, the law should be reviewed.
However, these tools are not necessarily used consistently at any level of government....