Leveraging Test-Driven Development (TDD) with Jest

Test-Driven Development has revolutionized how we approach software development. In this guide, we’ll explore how to effectively implement TDD using Jest, one of the most popular testing frameworks in the JavaScript ecosystem.

Understanding TDD Fundamentals

The core TDD cycle consists of three simple steps: Red (write a failing test), Green (make the test pass), and Refactor (improve the code while maintaining functionality).

Getting Started with Jest TDD

First, let’s set up a simple project:

npm init -y
npm install --save-dev jest

Update your package.json:

{
  "scripts": {
    "test": "jest --watchAll"
  }
}

Practical TDD Example

Let’s create a simple calculator module using TDD:

describe('Calculator', () => {
  test('should add two numbers correctly', () => {
    expect(calculator.add(2, 3)).toBe(5);
  });
});

Now implement the calculator:

const calculator = {
  add: (a, b) => a + b,
};

module.exports = calculator;

Best Practices for TDD with Jest

1. Keep tests focused and atomic
2. Use descriptive test names
3. Follow the Arrange-Act-Assert pattern
4. Maintain test isolation
5. Write the minimum code needed to pass tests

Advanced TDD Patterns

describe('Advanced Calculator', () => {
  beforeEach(() => {
    // Setup
  });

  test('should handle complex calculations', () => {
    const result = calculator.evaluate('2 + 3 * 4');
    expect(result).toBe(14);
  });
});