Phase 3: Property-Based Testing for AI Code · 60 min · Python · Hypothesis · pytest

Advanced PBT: Stateful Testing

Stateful systems have invariants too. The state machine never lies.

Real-world application: Engineers who understand stateful property testing can catch concurrency bugs in AI-generated code (like the 847 duplicate charges incident) that sequential unit tests fundamentally cannot detect.

What you will learn

Understand stateful property testing and RuleMachine
Test stateful systems AI generates (caches, databases, state machines)
Use concurrent strategies to detect race conditions
Understand how PBT with concurrent strategies would have caught the 847 duplicate charges bug

Introduction

Advanced PBT: Stateful Testing

Objective

Run stateful PBT on an AI-generated shopping cart (sequential) and cache (sequential + concurrent). Observe how stateful testing catches bugs that only manifest across sequences of operations, and how concurrent testing detects race conditions.

Stateful systems have invariants too. The state machine never lies.

Unlock the full lesson

You've read the first 2 sections. The rest of this lesson covers The Problem, The Concept, Build, Check Yourself, Key Terms & Next — plus a hands-on lab, quiz, and project artifact.

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