https://zhisme.com/tags/debugging/Recent content in Debugging on @zhisme :: signal over noiseHugoen-usWed, 10 Jun 2026 00:00:00 +0000https://zhisme.com/articles/ruby-constant-frozen-at-boot/Wed, 10 Jun 2026 00:00:00 +0000https://zhisme.com/articles/ruby-constant-frozen-at-boot/<p>I like interview questions that come from real incidents instead of a puzzle book. You can&rsquo;t google your way out of them, and the candidate&rsquo;s reasoning maps directly onto the job. This one came from a payment service. It looks trivial. It is not.</p> <p>I&rsquo;ve stripped the production code and rebuilt the same shape around a fake payment router. The bug is identical; the names are not.</p> <h2 id="the-question">The Question</h2> <blockquote> <p>Here is a class that routes payments to a gateway. Occasionally a charge is<br> written to the database with <code>method_id = NULL</code>, even though the payment method<br> clearly exists in the <code>payment_methods</code> table. No exception is raised. The only<br> thing that reliably fixes it is restarting the process. Find the bug.</p>