Why are incomplete mocks considered an anti-pattern?

Partial mocks hide structural assumptions and lead to silent failures where tests pass but the actual integration fails due to missing fields required by downstream code.

How does this skill prevent production code pollution?

It identifies and blocks the addition of methods to production classes that are only used for testing, suggesting they be moved to external test-utility files instead.

Does this skill support Test-Driven Development (TDD)?

Yes, it is specifically designed to reinforce TDD cycles by ensuring tests fail against real code first, preventing developers from adding unnecessary mocks.

What is the 'Iron Law' of mocking according to this skill?

The core principle is to test what the code actually does, not what the mocks do. It mandates verifying real behavior rather than asserting that a mock was called.

Testing Anti-Patterns Guard

Name: Testing Anti-Patterns Guard
Author: carlopezzuto

bycarlopezzuto

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Security & Testing

Prevents common testing mistakes like mocking internal behavior or polluting production code with test-only methods.

This skill acts as an expert reviewer and architectural guardrail to ensure high-quality test suites by identifying and preventing common testing pitfalls. It enforces 'Iron Laws' such as verifying real behavior instead of mock existence, keeping production classes clean of test-specific utilities, and ensuring mocks are complete and well-understood. By integrating gate functions into the development workflow, it helps developers follow strict TDD principles, resulting in more resilient, maintainable, and meaningful test coverage that doesn't break during refactoring.

Key Features

01Enforces completeness in mock data structures to match real API schemas.

02Encourages a TDD-first workflow to ensure tests verify real functional requirements.

03Provides interactive 'Gate Functions' to validate mocking decisions before implementation.

04Identifies assertions that test mock existence rather than actual behavior.

050 GitHub stars

06Prevents the addition of test-only methods to production source code classes.

Use Cases

01Training junior developers on high-standard testing culture and the dangers of partial mocks.

02Reviewing unit tests to ensure they are not 'brittle' due to over-mocking of internal components.

03Refactoring legacy production code to extract and move test-specific leakage into dedicated utilities.

What are Skills?·How to Install

Install with 🐟 Skill.Fish

npx skillfish add carlopezzuto/agents testing-anti-patterns

For use in Claude.ai and ChatGPT

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