Even test cases will run into data sharing issues.
amazingly enough the law is more clever than programmers assume it is, and the clever dodges programmers come up with tend to be seen through and just lead to jail time.
Prime Exhibit - https://en.wikipedia.org/wiki/Hans_Reiser
Then when it fell apart he dropped back to arguing he just looked guilty because he was too smart to look innocent or something https://yro.slashdot.org/story/08/02/23/2218256/hans-reiser-...
https://www.eastbaytimes.com/2010/08/02/review-from-a-report... >He thought he was smarter than everyone else, but ultimately he was not
However, I would ban surveys because they can lead people to vote for the wrong person due to social pressure.
On past projects we've recorded the time the user submitted a from (with a checked consent checkbox), but this doens't feel like rigorous proof.