A growth feature might raise the block rate — which test, and can you see it?
Test selectionMediumProblem. A new growth feature could increase how often users block or report contacts — a rare event (say ~0.5% of users). You need a guardrail test. Which statistical test do you use, and can a normal experiment even detect a rare-event change?
Before you reveal: say your answer out loud, as if you were in the real interview — get your reasoning across clearly first. There is no single correct answer: reading what the interviewer is really after and defending your own thinking is what makes an answer strong.