Claude

Overview Fixing a production bug involves more than just writing new code. The real challenge lies in **reproduction**. If you cannot replicate the failure, you cannot guarantee the fix works for the specific scenario reported by the user. By integrating Test-Driven Development (TDD) principles into AI agent workflows, we move from "guessing and checking" to verified engineering. This tutorial explores how to configure agents like Claude MD to follow a strict reproduce-first protocol. Prerequisites To follow this guide, you should understand: * **Basic PHP/Laravel**: The examples use the Laravel framework. * **Testing Fundamentals**: Familiarity with unit and integration tests. * **AI Agents**: Understanding how tools like Claude interact with local codebases. Key Libraries & Tools * **Claude MD / CodeX**: Developer-centric AI agents that can read, write, and execute terminal commands within your project. * **Pest PHP**: A graceful testing framework for Laravel used here to run regression tests. * **Claude 3.5 Sonnet / Opus**: The underlying LLMs that power the logic of the code exploration and fix generation. Code Walkthrough: The Fail-First Workflow Step 1: The Failing Test Instead of letting the AI jump straight to a fix, we instruct it to write a test that fails against the current buggy codebase. For a project bulk update missing a permission check, the test should attempt to update a project belonging to a different user. ```php // Example failing test generated by the agent it('prevents updating projects that do not belong to the user', function () { $user = User::factory()->create(); $otherUser = User::factory()->create(); $project = Project::factory()->create(['user_id' => $otherUser->id]); $response = $this->actingAs($user)->patch("/projects/{$project->id}", [ 'name' => 'Hacked Name' ]); $response->assertStatus(403); }); ``` Step 2: Verification of Failure The agent executes this test. Seeing the test return a `200 OK` or `500 Error` instead of the expected `403 Forbidden` confirms the bug is reproducible. Step 3: The Fix and Verification Once reproduced, the agent applies the fix—likely a simple ownership check in the controller—and reruns the same test. A passing result now provides a true regression suite. Syntax Notes When configuring Claude MD, your `guidelines.md` or prompt must be explicit. Use active instructions: "Investigate the codebase, then write a failing test first." Avoid vague requests like "Use sub-agents," as these often lead to complexity without clarity in the merge process. Tips & Gotchas * **Trust but Verify**: AI-generated tests can sometimes have logic errors. Always review the test assertions to ensure they match the real-world bug. * **Model Choice**: While GPT-4o and Opus handle test generation well, cheaper models like Sonnet may skip the testing phase unless your instructions are strictly enforced in the system prompt.