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name: avoiding-testing-anti-patterns description: AI agent identifies and fixes common testing anti-patterns that lead to flaky, slow, or unmaintainable test suites. Use when reviewing tests, debugging test failures, or improving test quality.

Avoiding Testing Anti-Patterns

Quick Start

1. Identify - Recognize anti-pattern category (flaky, implementation, over-mocking)
2. Assess Severity - Critical (fix now), High (fix soon), Medium (plan to fix)
3. Apply Fix - Use proper async handling, test behavior not implementation
4. Verify - Run tests in random order, ensure independence
5. Prevent - Add test smell detection to CI

Features

Common Patterns

Copy// FLAKY: Timing-dependent
await sleep(100);  // May not be enough
expect(result).toBe('processed');

// FIXED: Wait for condition
await waitFor(() => {
  expect(result).toBe('processed');
}, { timeout: 5000 });

// FLAKY: Shared state between tests
let sharedState = [];
it('test1', () => { sharedState.push('a'); });
it('test2', () => { expect(sharedState).toHaveLength(1); }); // Order-dependent!

// FIXED: Fresh state each test
beforeEach(() => { sharedState = []; });

// IMPLEMENTATION: Testing private state
expect(counter._count).toBe(1);

// BEHAVIOR: Testing public interface
expect(counter.getValue()).toBe(1);

// OVER-MOCKING: Everything mocked
const mockDb = { save: jest.fn() };
const mockPayment = { charge: jest.fn() };
// Only testing that mocks were called

// FIXED: Mock boundaries only
const testDb = await createTestDatabase();  // Real
const mockPayment = createMockPaymentProvider();  // External only

Copy# Anti-Pattern Severity Guide
CRITICAL (fix immediately):
- Flaky tests - Random failures destroy trust
- Testing implementation - Breaks on every refactor
- Hidden dependencies - Tests fail mysteriously

HIGH (fix soon):
- Slow tests - Hurt development velocity
- Test interdependence - Can't run in isolation
- Over-mocking - Tests pass but bugs slip through

MEDIUM (plan to fix):
- Poor naming - Tests don't document behavior
- Magic values - Unclear expected values
- Giant tests - Hard to understand

LOW (fix when touching):
- Commented tests - Remove or fix
- Duplicate tests - Consolidate

Best Practices

Related Skills

• developing-test-driven - TDD with proper patterns
• testing-with-vitest - Vitest testing framework
• testing-with-playwright - E2E testing patterns
• debugging-systematically - Debug flaky test failures