testing anti-patterns

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---
name: testing-anti-patterns
description: Never test mock behavior. Never add test-only methods to production classes. Understand dependencies before mocking. Language-agnostic principles with TypeScript/Jest and Python/pytest examples.
user-invocable: false
disable-model-invocation: true
when_to_use: when writing or changing tests, adding mocks, or tempted to add test-only methods to production code
version: 3.0.0
tags:
  - testing
  - typescript
  - javascript
  - python
  - pytest
  - jest
  - mocking
  - tdd
  - anti-patterns
progressive_disclosure:
  entry_point:
    summary: "Avoid testing mocks, test-only production methods, and incomplete mocking. Test real behavior, not mock behavior. Covers TypeScript/Jest and Python/pytest."
    when_to_use: "When writing tests, adding mocks, reviewing test failures, or tempted to add test-only methods to production code."
    quick_start: "1. Ask: 'Am I testing real behavior?' 2. Check: 'Is this method only for tests?' 3. Verify: 'Do I understand what I'm mocking?' 4. Confirm: 'Is my mock complete?' 5. Apply: TDD prevents these patterns"
  references:
    - core-anti-patterns.md
    - completeness-anti-patterns.md
    - detection-guide.md
    - tdd-connection.md
    - python-examples.md
related_skills:
  - toolchains-typescript-testing-jest
  - toolchains-typescript-testing-vitest
  - toolchains-python-testing-pytest
  - universal-debugging-systematic-debugging
  - universal-debugging-verification-before-completion
---

# 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
```

## Core Anti-Pattern Categories

### 1. Testing Mock Behavior
Asserting on mock elements instead of real behavior. **Fix:** Test real component or don't mock it.
**→** [core-anti-patterns.md](references/core-anti-patterns.md#anti-pattern-1-testing-mock-behavior)

### 2. Test-Only Methods in Production
Methods in production classes only used by tests. **Fix:** Move to test utilities.
**→** [core-anti-patterns.md](references/core-anti-patterns.md#anti-pattern-2-test-only-methods-in-production)

### 3. Mocking Without Understanding
Mocking without understanding dependencies/side effects. **Fix:** Understand first, mock minimally.
**→** [core-anti-patterns.md](references/core-anti-patterns.md#anti-pattern-3-mocking-without-understanding)

### 4. Incomplete Mocks
Partial mocks missing fields downstream code needs. **Fix:** Mirror complete API structure.
**→** [completeness-anti-patterns.md](references/completeness-anti-patterns.md#anti-pattern-4-incomplete-mocks)

### 5. Tests as Afterthought
Implementation "complete" without tests. **Fix:** TDD - write test first.
**→** [completeness-anti-patterns.md](references/completeness-anti-patterns.md#anti-pattern-5-tests-as-afterthought)

## Quick Detection Checklist

Run this checklist before committing any test:

**Language-agnostic checks:**
```
□ Am I asserting on mock behavior instead of real behavior?
  → TypeScript: testId='*-mock', expect(mock).toHaveBeenCalled()
  → Python: mock.assert_called(), mock.call_count
  → If yes: STOP - Test real behavior or unmock

□ Does