Code Design: Chapter 2 - Development Methodologies

Introduction

Software development methodologies help organize and optimize the process of building software. They shape how teams approach coding, testing, and collaboration, ultimately leading to higher-quality software with lower maintenance costs. Here’s a breakdown of key methodologies with their core concepts and benefits.

TDD (Test-Driven Development

Write tests before coding each feature or function, building code around the tests to meet predefined expectations.

Benefits: Reduces bugs, promotes a test-first mindset, and encourages a high standard of code quality.

// Test (written before code)
test('should add two numbers', () => {
  expect(add(2, 3)).toBe(5);
});

// Code (written to pass the test)
function add(a: number, b: number): number {
  return a + b;
}

BDD (Behavior-Driven Development)

Focuses on the behavior of an application from the user’s perspective, using readable scenarios to outline expected behaviors.

Benefits: Enhances collaboration between technical and non-technical team members by using human-readable tests that bridge the communication gap.

// Scenario written in a readable format (BDD style)
// "Given a user logs in, when they add an item to the cart, then the cart count should increase by 1."

test('should increase cart count by 1 when an item is added', () => {
  user.login();
  user.addToCart(item);
  expect(user.cart.count).toBe(1);
});

DDD (Domain-Driven Design)

Models software closely around the business domain, making the code reflect the business logic and structure. DDD is especially useful in complex applications.

Key Concepts: Domains, sub-domains, entities, and value objects help create a shared language between developers and domain experts.

Benefits: Keeps code aligned with business needs, making it easier to adapt and manage complex systems over time.

// Defining a 'Student' as an entity with unique characteristics relevant to the domain.

class Student extends User {
  constructor(public email: string, public name: string) {}
  joinGroup(groupID: string) {
      // Logic to attch the student to a group
  }
}

const groupA = new Group('group-a');
const student = new Student('alice@student.com', 'Alice');
student.joinGroup(groupA.id);

Event-Driven Development

Organizes applications around events that trigger actions in response to specific occurrences (e.g., user actions or system updates), making components decoupled and responsive to state changes.

Benefits: Increases scalability and flexibility, especially in complex workflows or real-time applications.

This kind of architecture is used in Real-time NoSQL databases like Firebase.

// Event-based system example
interface Event {
  eventSignature: string;
  data: any;
}

class EventBus {
  private listeners: { [signature: string]: Function[] } = {};

  subscribe(eventSignature: string, callback: Function) {
    if (!this.listeners[eventSignature]) this.listeners[eventSignature] = [];
    this.listeners[eventSignature].push(callback);
  }

  publish(event: Event) {
    const callbacks = this.listeners[event.eventSignature];
    if (callbacks) callbacks.forEach(callback => callback(event.data));
  }
}

const eventBus = new EventBus();

// It will only be triggred when it's published
eventBus.subscribe('userRegistered', (data) => {
  console.log(`Welcome email sent to ${data.email}`);
});

eventBus.publish({ type: 'userRegistered', data: { email: 'user@example.com' } });

Summary

Each of these methodologies brings unique advantages, supporting developers and teams to manage code quality, complexity, and collaboration. TDD and BDD enforce a testing-first approach, helping teams catch issues early. DDD aligns code with the business, making it more comprehensible and adaptable. Event-Driven Development improves system flexibility, allowing for highly responsive and decoupled components. Together, they form a toolkit that can adapt to various project needs and complexities, especially in large, dynamic applications.

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Series Chapters

1. Introduction

2. Chapter 1 - Design Principles

3. Chapter 2 - Development Methodologies

4. Chapter 3 - Architectural Patterns

5. Chapter 4 - Coding Standards and Best Practices