Testing Anti-Patterns Guide

What problem does it solve?

This document identifies three foundational rules for effective testing and outlines five major anti-patterns to avoid.

Core Principles

The core guidance emphasizes that "Tests must verify real behavior, not mock behavior." Mocks are a means to isolate, not the thing being tested.

The document identifies five major anti-patterns:

• Testing Mock Behavior: Asserting that mocks exist rather than verifying real component output represents a fundamental test failure.
• Test-Only Methods: Adding methods like destroy() solely for test cleanup pollutes production code. Instead, place cleanup logic in dedicated test utilities.
• Mocking Without Understanding: Over-mocking to "be safe" often breaks critical test logic by replacing methods whose side effects the test depends upon. Understanding dependency chains before mocking is essential.
• Incomplete Mocks: Partial mock objects create false confidence—they pass tests while failing in real integration when code accesses unmocked fields.
• Integration Tests as Afterthought: TDD prevents this by writing tests first, which naturally surfaces what actually needs mocking versus what should remain real.

Prevention Strategy

Test-Driven Development inherently prevents these anti-patterns by forcing developers to observe tests fail against real implementations before adding mocks. This process reveals whether mocks are genuinely needed or whether complex mock setups suggest reconsidering the testing approach entirely.

Quick Start

Review a failing test suite to identify mocks and anti-patterns, remove test-only methods, and ensure tests verify real behavior rather than mocks.