I wrote some software to handle charging customer's credit cards. It worked fine in the dev environment so a week later we deployed it since we hadn't been charging customers at all until that point. We would run bills once a day until all the unprocessed billing was caught up.
Well, in dev, the database was refreshed with prod data every night at midnight, so we never saw the bug in my code. I had a sign error in updating the customer's balance so instead of lowering their balance by the payment amount, my code increased their balance. Geometric growth is an amazing thing. A few days later we had calls from angry customers because we had maxed out their credit cards. Miraculously, I was not fired. In retrospect, I think that it might have been because the manager would have then had to explain why he had not made sure there was not adequate testing on something so central to the business.
Well, in dev, the database was refreshed with prod data every night at midnight, so we never saw the bug in my code. I had a sign error in updating the customer's balance so instead of lowering their balance by the payment amount, my code increased their balance. Geometric growth is an amazing thing. A few days later we had calls from angry customers because we had maxed out their credit cards. Miraculously, I was not fired. In retrospect, I think that it might have been because the manager would have then had to explain why he had not made sure there was not adequate testing on something so central to the business.