How a 1% bug survived 400 test rounds and why random sampling failed to catch it

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A developer shipping a blockchain betting game called Replay discovered a critical bug that only triggered on 1.01% of rounds — specifically when a player hit the highest-value 96.03× ticket. Random playtesting across 400 rounds never surfaced the flaw, since the statistical odds of missing it that many times were about 1.7%, making the absence of failure uninformative rather than reassuring. The bug caused every transaction involving the top-ranked ticket to revert, because a single wei discrepancy between independently derived payout values violated the casino platform's strict payout cap. The developer ultimately solved the problem not by playing more rounds, but by exploiting two contract properties — a pure settlement function and a deterministic draw mechanism — to exhaustively simulate all 1,287 possible orderings in seconds via a script. This deterministic sweep confirmed exactly 13 winning ranks matched the mathematical expectation, proving correctness across the entire outcome space rather than relying on luck-based sampling.

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