Why timing matters.
WHAT DETERMINES COST
When the defect is found, relative to when it was introduced.
WHAT FINDING IT AT WRITING COSTS
The time to correct a thought.
WHAT FINDING IT IN REVIEW COSTS
A conversation.
WHAT FINDING IT IN TESTING COSTS
Reproduction, diagnosis, correction, and retesting.
WHAT FINDING IT IN PRODUCTION COSTS
All of that, plus support, plus affected users, plus an emergency release.
WHAT THE ADDITIONAL COSTS ARE
Context lost, since the author has moved on Other work built on the defect Data possibly corrupted Trust damaged
WHY DATA CORRUPTION IS THE WORST
The defect can be fixed; the data may not be recoverable.
WHAT THAT ARGUES FOR
Validation at boundaries, and testing anything that writes.
WHAT SHIFTING LEFT MEANS
Moving testing earlier in the process.
WHAT IT INVOLVES PRACTICALLY
Reviewing requirements for testability Writing tests alongside code Running checks on every change Static analysis
WHAT SHIFTING RIGHT MEANS
Continuing to verify in production.
WHAT THAT INVOLVES
Monitoring Gradual rollout Feature flags Testing against production behaviour
WHAT TO DO
Both, since neither alone suffices.
