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AI testing can be far more exhaustive than human testing because AI does not default to following the happy path, as demonstrated when Codex immediately found a blocking bug in an onboarding flow that had survived for months.
Claire describes how Codex's automated browser testing uncovered a blocking bug in her onboarding flow that had survived for months — because as a human tester she always unconsciously followed the happy path. ✦ AI generated
Claire · Lenny's Newsletter · 2026-07-27 · original ↗
When Claire tests her own onboarding flow, she naturally follows the happy path. She fills out every required field, clicks 'next,' and never intentionally tries to break anything. Codex tested the flow as both a team and an individual, pushed on required-field edge cases, and immediately uncovered a blocking bug that had survived for months simply because Claire always completed the form correctly.
Read full article ↗excerpt · fair-use quotation
- ·Human testers unconsciously follow the happy path
- ·Claire never intentionally tries to break her own flow
- ·AI tests edge cases humans naturally avoid
- ·Codex pushed on required-field edge cases as individual and team
- ·It immediately uncovered a blocking bug
- ·That bug had survived for months of human testing
- ·Claire always filled every required field and clicked next
- ·She never deviated from correct form entry
- ·AI caught what the happy path had hidden for months
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In practice · 2
Frontier AI cyber models don't create vulnerabilities — they discover bugs that already exist in code written by humans; getting these tools into defenders' hands before attackers will harden infrastructure, not weaken itDavid Sacks · All-In Podcast · conf 80%Persona testing with browser use — having AI use a product as a specific persona like a PM coming out of a meeting — can reveal structural friction that synthetic user research misses.Claire · Lenny's Newsletter · conf 65%