Trading Bot Passed All Tests but Lost Money Due to Timezone Oversight

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A developer building a public automated stock trading bot discovered a costly bug after deploying code that had passed every unit test. The bot's end-of-day routine used the server's UTC clock instead of Eastern Time, causing it to execute trades based on incomplete market data. Because the tests relied on fixed, hand-crafted timestamps rather than real-world conditions, the timezone mismatch was never caught before deployment. The incident highlighted a key limitation of unit testing: a green test suite confirms code consistency, not real-world correctness. The developer has since updated tests to include messy, realistic inputs such as wrong timezones, missing data, and market holidays.

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MeshCtx v3.131 Ships Full Hebrew RTL Support Across 11 Languages With CI Testing

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ProgrammingDEV Community ·

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ProgrammingDEV Community ·

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