Introduction

Writing effective tests is crucial for successful Test-Driven Development. This article explores best practices that will help you write better tests and improve your TDD workflow.

Test Structure: The AAA Pattern

The Arrange-Act-Assert (AAA) pattern is a fundamental structure for writing clear and maintainable tests:


test('should calculate total with discount', () => {
    // Arrange
    const calculator = new PriceCalculator();
    const price = 100;
    const discount = 0.1;

    // Act
    const total = calculator.calculateTotal(price, discount);

    // Assert
    expect(total).toBe(90);
});

Test Naming Conventions

Good test names should clearly describe the behavior being tested:

  • Use descriptive names that explain the behavior
  • Follow a consistent pattern (e.g., "should [expected behavior] when [condition]")
  • Avoid implementation details in test names

Test Isolation

Each test should be independent and not rely on the state from other tests:

  • Set up fresh test data for each test
  • Clean up after tests
  • Avoid shared state between tests

Test Coverage

While 100% coverage isn't always necessary, it's important to test:

  • Happy path scenarios
  • Edge cases
  • Error conditions
  • Boundary conditions

Code Examples

Good Test Example


describe('UserService', () => {
    test('should create user with valid data', () => {
        // Arrange
        const userData = {
            name: 'John Doe',
            email: 'john@example.com'
        };
        const userService = new UserService();

        // Act
        const user = userService.createUser(userData);

        // Assert
        expect(user).toHaveProperty('id');
        expect(user.name).toBe(userData.name);
        expect(user.email).toBe(userData.email);
    });

    test('should throw error with invalid email', () => {
        // Arrange
        const userData = {
            name: 'John Doe',
            email: 'invalid-email'
        };
        const userService = new UserService();

        // Act & Assert
        expect(() => userService.createUser(userData))
            .toThrow('Invalid email format');
    });
});

Common Anti-patterns to Avoid

  • Testing implementation details
  • Over-mocking dependencies
  • Writing brittle tests
  • Ignoring test maintenance

Conclusion

Following these best practices will help you write more maintainable and effective tests, leading to better software quality and a more efficient development process.

"The act of writing a unit test is more an act of design than of verification. It is also more an act of documentation than of verification." - Robert C. Martin