Test Driven Development in Action with JS

 

Why Test? A Developer's Guide to Test-Driven Development

The Power of Testing in Interviews

Imagine you're sitting in a technical interview for an entry-level web developer job and they ask you to implement a complex algorithm. Instead of panicking, you can say:

"No problem, let me write a few test cases for that first."

This buys you time and makes you look professional. Test-driven development (TDD) is a technique where you describe behavior before implementation.

Test-Driven Development Philosophy

The TDD mantra is Red → Green → Refactor:

1. Red: Write a failing test first
2. Green: Write code to make it pass
3. Refactor: Optimize your code

While not always practical, TDD can improve productivity when requirements are clear.

Testing Strategies

Functional Testing

• Unit Testing: Validate individual functions/methods
• Integration Testing: Test how multiple units work together
• End-to-End Testing: Simulate actual user behavior

Other Important Terms

• Acceptance Testing
• System Testing
• Smoke/Sanity Testing

Non-Functional Testing

Tests for performance, usability, and security rather than code functionality.

Hands-On: Implementing a Stack with Jest

Setting Up Jest

npm install jest
// package.json
"scripts": {
  "test": "jest --watchAll --verbose"
}

Writing Your First Test

describe('Stack', () => {
  test('should be created empty', () => {
    const stack = new Stack();
    expect(stack.top).toBe(-1);
    expect(stack.items).toEqual({});
  });
});

Setup & Teardown

let stack;

beforeEach(() => {
  stack = new Stack();
});

End-to-End Testing with Cypress

Cypress provides browser-based testing that simulates real user interactions:

describe('Form Submission', () => {
  it('can fill out a form', () => {
    cy.visit('/');
    cy.get('input[name="email"]')
      .type('user@example.com')
      .should('have.value', 'user@example.com');
    cy.get('form').submit();
  });
});

Install with: npm install cypress

Final Thoughts

Testing walks a fine line between valuable and wasteful. The key is knowing:

• When to test (clear requirements = good candidate)
• What to test (focus on critical paths)
• How much to test (balance coverage with productivity)

Start with small unit tests, then explore end-to-end testing for the most valuable coverage.