systematic-debugging

Root cause analysis for test failures requires reproducing the bug reliably, characterizing expected versus actual behavior, and testing one variable at a time. You form and falsify hypotheses until isolating the true root cause, then ship a fix with a regression test.

Debug flaky production-only issues by creating a minimal reproduction case and using log-driven debugging. When timeline-based, apply git bisect to perform commit-range binary search, turning unpredictable incidents into deterministic investigations.

Systematically debug behavior changes after a refactor by first reproducing the failure, then isolating the smallest changing factor. Use one-variable-at-a-time testing or git bisect to locate the exact commit causing the regression.

Use git bisect for debugging when a failure is timeline-based, such as behavior that worked yesterday but broke today. It performs commit-range binary search to pinpoint the exact commit introducing the bug, turning "it worked before" into a deterministic investigation.

Bug fixes keep coming back when symptom-suppression occurs instead of root-cause fixing. Prevent recurring issues by isolating the true root cause through hypothesis testing, implementing a root-cause fix, and adding a regression test that fails without the fix.

Hypothesis testing diagnoses both deterministic and flaky failures by applying a stepwise debugging loop. You reproduce the issue, form testable hypotheses about the root cause, and falsify them with one-variable changes until the root cause is named.