Digging DeeperTest-Driven Development

Test-Driven Development (TDD)

What is Test-Driven Development?

Test-Driven Development (TDD) is a software development methodology that follows a short, repeating cycle of steps:

  1. Write a failing test
  2. Write the simplest code to make the test pass
  3. Refactor the code while keeping the test passing

Why Use TDD?

1. Improved Code Quality

  • Reduces software bugs
  • Leads to better code design
  • Provides automatic documentation for expected behavior

2. Increased Confidence

  • Ensures the code works as expected
  • Makes it easier to detect errors
  • Reduces risks associated with changes

3. Enhanced Productivity

  • Reduces debugging time
  • Speeds up the development process
  • Simplifies maintenance

TDD Cycle in Detail

Step 1: The Test (Red)

  • Write a test that describes the desired behavior
  • Ensure the test fails
  • Clearly define the requirements

Step 2: The Code (Green)

  • Write the simplest code to pass the test
  • Focus only on functionality
  • Do not worry about performance or elegance

Step 3: Refactoring (Refactor)

  • Refactor the code while ensuring tests still pass
  • Remove duplication
  • Improve readability and maintainability

Types of Tests in TDD

1. Unit Tests

Tests small, isolated parts of the code

describe('Add function', () => {
    test('adds two positive numbers', () => {
        expect(add(2, 3)).toBe(5);
    });
});

2. Integration Tests

Tests the interaction between multiple units

describe('User service', () => {
    test('register and login', async () => {
        const user = await UserService.register(userData);
        const login = await UserService.login(credentials);
        expect(login.success).toBe(true);
    });
});

3. Behavioral Tests

Tests behavior from a user’s perspective

describe('User registration', () => {
    test('shows success message upon registration', async () => {
        const response = await registerUser(validData);
        expect(response.message).toBe('Registration successful');
    });
});

Best Practices in TDD

1. Test Design

  • Small, focused tests
  • Descriptive and clear names
  • Sufficient coverage for all cases

2. Writing Code

  • Start with simple cases
  • Gradually move towards complexity
  • Stick to the TDD cycle

3. Continuous Improvement

  • Regularly review the code
  • Update tests when necessary
  • Improve coverage

Practical Example in Kawkab

1. Write the Test First

// tests/services/auth.test.ts
describe('AuthService', () => {
    test('validates password', () => {
        const auth = new AuthService();
        expect(auth.validatePassword('123456')).toBe(false);
        expect(auth.validatePassword('StrongPass123!')).toBe(true);
    });
});

2. Implement the Code

// src/services/auth.ts
export class AuthService {
    validatePassword(password: string): boolean {
        return password.length >= 8 &&
               /[A-Z]/.test(password) &&
               /[0-9]/.test(password) &&
               /[!@#$%^&*]/.test(password);
    }
}

3. Refactor the Code

// src/services/auth.ts
export class AuthService {
    private readonly MIN_LENGTH = 8;
    private readonly PATTERNS = {
        uppercase: /[A-Z]/,
        numbers: /[0-9]/,
        special: /[!@#$%^&*]/
    };
 
    validatePassword(password: string): boolean {
        return this.hasMinLength(password) &&
               this.meetsAllCriteria(password);
    }
 
    private hasMinLength(password: string): boolean {
        return password.length >= this.MIN_LENGTH;
    }
 
    private meetsAllCriteria(password: string): boolean {
        return Object.values(this.PATTERNS)
            .every(pattern => pattern.test(password));
    }
}

Conclusion

Test-Driven Development in Kawkab:

  • Ensures code quality and reliability
  • Eases maintenance and development
  • Provides automatic documentation
  • Increases developer confidence in changes

We recommend using TDD in Kawkab projects to ensure:

  • More robust code
  • Faster development
  • Easier maintenance
  • Better documentation
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