Testing Anti Patterns

This is one of those skills that catches you doing the thing you know you shouldn't do but do anyway. It pushes back when you're mocking too much or testing mock behavior instead of real code behavior. The core principle is simple: test what the code does, not what the mocks do. It activates when you're writing tests, adding mocks, or about to add test-only methods to your production code. Works best if you're already following TDD, and it pairs with bobmatnyc's separate TDD skill. Think of it as a linter for your testing habits rather than your code.

skills.sh installs: 226
GitHub stars: 79
last updated: Aug 21, 2026

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Install

$ npx -y skills add bobmatnyc/claude-mpm-skills --skill 'Testing Anti-Patterns' --agent claude-code

Installs into .claude/skills of the current project.

Files

Testing Anti-Patterns

Overview

Tests must verify real behavior, not mock behavior. Mocks are a means to isolate, not the thing being tested.

Core principle: Test what the code does, not what the mocks do.

Following strict TDD prevents these anti-patterns. See the Test-Driven Development skill (available in the skill library) for the complete TDD workflow.

When to Use This Skill

Activate this skill when:

Writing or changing tests - Verify tests cover real behavior
Adding mocks - Ensure mocking is necessary and correct
Reviewing test failures - Check if mock behavior is the issue
Tempted to add test-only methods - STOP and reconsider
Tests feel overly complex - Sign of over-mocking

The Iron Laws

1. NEVER test mock behavior
2. NEVER add test-only methods to production classes
3. NEVER mock without understanding dependencies
4. NEVER create incomplete mocks
5. NEVER treat tests as afterthought