testing-best-practices

majiayu000's avatarfrom majiayu000

Testing methodologies, patterns, and best practices for unit, integration, and E2E tests. (project)

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[Testing and QA]

When & Why to Use This Skill

This Claude skill provides a comprehensive framework for software testing, encompassing unit, integration, and E2E testing methodologies. It offers standardized patterns like AAA (Arrange, Act, Assert), advanced mocking strategies, and architectural best practices to help developers ensure code reliability, maintainability, and high performance.

Use Cases

  • Standardizing unit test structures using the AAA pattern to improve readability and maintenance across development teams.
  • Implementing robust mocking and spying strategies for complex dependencies to isolate logic during testing.
  • Designing integration tests for APIs and databases to verify seamless communication between system components.
  • Setting up end-to-end (E2E) testing workflows with Playwright to validate critical user journeys and UI stability.
  • Optimizing software quality by establishing code coverage targets and identifying high-priority edge cases for testing.
nametesting-best-practices
descriptionTesting methodologies, patterns, and best practices for unit, integration, and E2E tests. (project)
allowed-toolsRead, Grep, Glob, Edit, Write, Bash

Testing Best Practices

Testing Pyramid

        /\
       /E2E\        <- Few, slow, expensive
      /------\
     /Integration\  <- Some, moderate speed
    /--------------\
   /   Unit Tests   \ <- Many, fast, cheap
  /------------------\

Unit Testing

AAA Pattern

describe('Calculator', () => {
  it('should add two numbers correctly', () => {
    // Arrange
    const calculator = new Calculator();

    // Act
    const result = calculator.add(2, 3);

    // Assert
    expect(result).toBe(5);
  });
});

Naming Convention

// Pattern: should [expected behavior] when [condition]
it('should throw error when dividing by zero')
it('should return empty array when no items match')
it('should update user when valid data provided')

Test Organization

describe('UserService', () => {
  describe('createUser', () => {
    it('should create user with valid data')
    it('should throw error when email exists')
    it('should hash password before saving')
  });

  describe('deleteUser', () => {
    it('should remove user from database')
    it('should throw error when user not found')
  });
});

Mocking

Function Mocks

const mockFn = jest.fn();
mockFn.mockReturnValue('value');
mockFn.mockResolvedValue('async value');
mockFn.mockRejectedValue(new Error('fail'));

Module Mocks

jest.mock('./database', () => ({
  query: jest.fn().mockResolvedValue([]),
}));

Spy on Methods

const spy = jest.spyOn(service, 'method');
expect(spy).toHaveBeenCalledWith(arg1, arg2);

Integration Testing

API Testing

describe('POST /api/users', () => {
  it('should create a new user', async () => {
    const response = await request(app)
      .post('/api/users')
      .send({ name: 'John', email: 'john@example.com' })
      .expect(201);

    expect(response.body.data.name).toBe('John');
  });
});

Database Testing

beforeEach(async () => {
  await db.migrate.latest();
  await db.seed.run();
});

afterEach(async () => {
  await db.migrate.rollback();
});

E2E Testing

Playwright Example

test('user can login', async ({ page }) => {
  await page.goto('/login');
  await page.fill('[name="email"]', 'user@example.com');
  await page.fill('[name="password"]', 'password123');
  await page.click('button[type="submit"]');
  await expect(page).toHaveURL('/dashboard');
});

Code Coverage

Coverage Targets

  • Statements: 80%+
  • Branches: 75%+
  • Functions: 80%+
  • Lines: 80%+

Focus Areas

  • Critical business logic
  • Edge cases and error handling
  • Security-sensitive code

Don't Over-Test

  • Getters/setters
  • Framework code
  • Third-party libraries
  • Simple transformations

Test Data

Factories

const createUser = (overrides = {}) => ({
  id: faker.string.uuid(),
  name: faker.person.fullName(),
  email: faker.internet.email(),
  ...overrides,
});

Fixtures

// fixtures/users.json
{
  "admin": { "id": "1", "role": "admin" },
  "user": { "id": "2", "role": "user" }
}