Phase 1: Test-Driven AI Development · 50 min · Python · pytest · Hypothesis

Behavioral Contracts: Constraining AI Code Generation

Contracts are the guardrails. The AI can drive, but it stays on the road.

Real-world application: Engineers who can define behavioral contracts with preconditions, postconditions, and invariants demonstrate design-by-contract thinking -- a skill that becomes critical when AI generates the implementation and the contract is the only automated check that the implementation is correct.

What you will learn

Define behavioral contracts with preconditions, postconditions, and invariants
Express contracts as pytest fixtures and Hypothesis invariants
Use contract violations as test failures that constrain AI code generation
Distinguish contract-based testing from example-based testing

Introduction

Behavioral Contracts: Constraining AI Code Generation

Objective

Define a behavioral contract (preconditions, postconditions, invariants) for a function, use an AI assistant to generate the implementation, and enforce the contract with Hypothesis-based invariant tests.

Contracts are the guardrails. The AI can drive, but it stays on the road.

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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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