Example◆Article · 36:58 — 38:58
Amazon used TLA+ to find a bug whose shortest error trace was 35 steps — a bug that would have been impossible to find through conventional testing.
The AWS team documented a case where TLA+ found a deeply hidden bug requiring a 35-step error trace to exhibit, which had passed through design review, code review, and testing undetected. ✦ AI generated
Hillel Wayne · The Pragmatic Engineer · 2026-07-29 · original ↗
Amazon used TLA+ to find a bug almost impossible to locate without formal methods. In the paper How AWS uses formal methods, the AWS team shared that they'd found a complicated bug for which the shortest error trace to exhibit was 35 steps (!!). The bug passed unnoticed through extensive design review, code reviews, and testing. AWS concluded they wouldn't have uncovered it if they'd stuck to conventional testing approaches.
Read full article ↗excerpt · fair-use quotation
- ·Shortest error trace was 35 steps deep
- ·Bug passed design review, code review, and testing
- ·AWS: testing alone would never have uncovered it
- ·Conventional testing cannot reach 35-step traces
- ·Deep bugs hide beyond practical testing depth
- ·Formal methods find what reviews and tests miss
Around this claim