Testing Anti-Patterns

Overview

Tests must validate real behavior, not mock behavior. Mocks are isolation tools; they are never the subject under test. Follow these guardrails whenever you touch tests or mocks.

Iron Laws

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

Anti-Pattern 1: Testing Mock Behavior

• ❌ Example: asserting getByTestId('sidebar-mock') exists after mocking <Sidebar/>.
• Why wrong: proves mock works, says nothing about component.
• ✅ Fix: test the real component (or mock only for isolation but assert behavior, not mock internals).