testing

Testing Standards Skill

Level 1: Quick Start (5 minutes)

What You'll Learn

Implement effective testing strategies to ensure code quality, catch bugs early, and maintain confidence in changes.

Core Principles

• Test First: Write tests before implementation (TDD)
• Coverage: Aim for >80% code coverage
• Isolation: Tests should be independent and repeatable
• Speed: Keep unit tests fast (<100ms each)

Testing Pyramid

      /\
     /  \  E2E Tests (Few)
    /----\
   / Inte \
  / gration \ (Some)
 /  Tests   \
/------------\
/ Unit Tests  \ (Many)
/--------------\

Quick Start Example

// 1. Write the test first (RED)
describe("calculateDiscount", () => {
  it("should apply 10% discount for premium users", () => {
    const user = { tier: "premium" };
    const order = { total: 100 };

    const result = calculateDiscount(user, order);

    expect(result).toBe(90);
  });
});

// 2. Implement minimal code (GREEN)
function calculateDiscount(user, order) {
  if (user.tier === "premium") {
    return order.total * 0.9;
  }
  return order.total;
}

// 3. Refactor (REFACTOR)
function calculateDiscount(
  user: User,
  order: Order
): number {
  const PREMIUM_DISCOUNT = 0.1;
  return user.tier === "premium"
    ? order.total * (1 - PREMIUM_DISCOUNT)
    : order.total;
}

Essential Checklist

• Unit tests for all business logic
• Integration tests for critical paths
• Tests run in CI/CD pipeline
• Coverage >80%
• Tests are maintainable and readable

Common Pitfalls

• Testing implementation details instead of behavior
• Slow tests that discourage running them
• Flaky tests that fail intermittently
• Poor test isolation (shared state)

---

Level 2: Implementation (30 minutes)

Deep Dive Topics

1. Test-Driven Development (TDD)

Red-Green-Refactor Cycle:

// STEP 1: RED - Write failing test
describe("UserService", () => {
  describe("createUser", () => {
    it("should hash password before saving", async () => {
      const userData = {
        email: "[email protected]",
        password: "SecurePass123!",
      };

      const service = new UserService(mockRepository, mockHasher);
      await service.createUser(userData);

      expect(mockHasher.hash).toHaveBeenCalledWith("SecurePass123!");
      expect(mockRepository.save).toHaveBeenCalledWith(
        expect.objectContaining({
          email: "[email protected]",
          passwordHash: expect.any(String),
        })
      );
    });
  });
});

// STEP 2: GREEN - Minimal implementation
class UserService {
  constructor(
    private repository: UserRepository,
    private hasher: PasswordHasher
  ) {}

  async createUser(userData: UserData): Promise<User> {
    const passwordHash = await this.hasher.hash(userData.password);
    return this.repository.save({
      ...userData,
      passwordHash,
    });
  }
}

// STEP 3: REFACTOR - Improve design
class UserService {
  constructor(
    private repository: UserRepository,
    private hasher: PasswordHasher,
    private validator: UserValidator
  ) {}

  async createUser(userData: UserData): Promise<User> {
    await this.validator.validate(userData);
    const passwordHash = await this.hasher.hash(userData.password);

    const user = new User({
      email: userData.email,
      passwordHash,
      createdAt: new Date(),
    });

    return this.repository.save(user);
  }
}