When should I use the gate functions included in this skill?

You should apply the gate functions before asserting on any mock, before adding a new method to a production class, and before deciding to mock any specific dependency or service.

What are the 3 Iron Laws of testing enforced by this skill?

The 3 Iron Laws are: 1. Never test mock behavior (test real component behavior instead), 2. Never add test-only methods to production (use test utilities), and 3. Never mock without understanding dependencies.

Does this skill work with languages other than Rust?

While the examples provided are in Rust, the principles and gate functions are language-agnostic and apply to any object-oriented or functional programming environment using mocks and unit tests.

How does this skill prevent production code pollution?

It uses a gate function that triggers before a method is added to a production class. If the method is only used for testing (like a reset or cleanup method), the skill directs the developer to place it in a test utility module instead.

Testing Anti-Patterns Guard

Name: Testing Anti-Patterns Guard
Author: withzombies

bywithzombies

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Security & Testing

Enforces rigorous testing standards by preventing brittle mocks, production code pollution, and misunderstood dependency isolation.

The Testing Anti-Patterns skill serves as an architectural guardrail for developers using Claude Code, ensuring that test suites remain robust and production code stays clean. It implements three 'Iron Laws'—never testing mock behavior, prohibiting test-only methods in production source, and requiring full understanding of dependencies before mocking. By applying specific gate functions during the coding process, it helps engineers avoid common pitfalls like false-positive tests and 'leaky' APIs, ultimately leading to more maintainable and reliable software systems.

Key Features

01Provides pre-action Gate Functions to validate assertions and mocking strategies

0258 GitHub stars

03Detects and blocks the addition of test-only methods like reset() to production classes

04Enforces the 3 Iron Laws of testing to eliminate brittle and deceptive test suites

05Guides developers to mock at the correct level of abstraction (e.g., I/O vs. business logic)

06Includes specific code examples for identifying and correcting common testing anti-patterns

Use Cases

01Refactoring complex test suites where excessive mocking has obscured the actual logic being tested

02Reviewing and refining new unit tests to ensure they verify real behavior instead of mock state

03Maintaining production code purity by redirecting test-specific utilities to dedicated test helper modules

What are Skills?·How to Install

Install with 🐟 Skill.Fish

npx skillfish add withzombies/hyperpowers testing-anti-patterns

For use in Claude.ai and ChatGPT

Download Skill