Automated Testing

Automated testing is the most critical quality gate in a CI/CD pipeline. Without reliable tests, you cannot confidently ship changes. This lesson covers testing levels, strategies, and how to integrate tests into your pipeline.

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Why Automated Testing?

Manual testing is:

• Slow — humans take minutes to hours
• Error-prone — repetitive tasks lead to mistakes
• Unscalable — cannot run on every commit
• Expensive — requires dedicated QA time

Automated testing is:

• Fast — thousands of tests in seconds
• Consistent — same result every time
• Scalable — runs on every push, every PR
• Cheap — once written, runs forever

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The Testing Pyramid

The testing pyramid is a widely accepted model for balancing different types of tests:

         ╱╲
        ╱ E2E ╲          Few, slow, expensive
       ╱────────╲
      ╱Integration╲      Some, moderate speed
     ╱──────────────╲
    ╱   Unit Tests   ╲   Many, fast, cheap
   ╱──────────────────╲

Level	Quantity	Speed	Cost	Scope
Unit	Many (hundreds+)	Very fast (ms)	Low	Single function / class
Integration	Some (tens)	Moderate (seconds)	Medium	Multiple components
End-to-End (E2E)	Few (< 20)	Slow (minutes)	High	Full user workflow

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Types of Tests

Unit Tests

Test a single function, method, or component in isolation. Dependencies are mocked.

// sum.ts
export function sum(a: number, b: number): number {
  return a + b;
}

// sum.test.ts
import { sum } from './sum';

describe('sum', () => {
  it('adds two positive numbers', () => {
    expect(sum(2, 3)).toBe(5);
  });

  it('handles negative numbers', () => {
    expect(sum(-1, 1)).toBe(0);
  });

  it('handles zero', () => {
    expect(sum(0, 0)).toBe(0);
  });
});

Integration Tests

Test how multiple components work together — e.g., API routes with a database.

// api.test.ts
import { createServer } from '../server';
import { prisma } from '../db';

describe('POST /api/users', () => {
  afterAll(() => prisma.$disconnect());

  it('creates a user and returns 201', async () => {
    const app = createServer();
    const res = await app.inject({
      method: 'POST',
      url: '/api/users',
      payload: { name: 'Alice', email: 'alice@example.com' },
    });

    expect(res.statusCode).toBe(201);
    expect(res.json()).toMatchObject({ name: 'Alice' });
  });
});

End-to-End (E2E) Tests

Test the full application from the user's perspective, typically using a browser.

// login.e2e.ts (Playwright)
import { test, expect } from '@playwright/test';

test('user can log in', async ({ page }) => {
  await page.goto('http://localhost:3000/login');
  await page.fill('[name="email"]', 'alice@example.com');
  await page.fill('[name="password"]', 'secret123');
  await page.click('button[type="submit"]');
  await expect(page).toHaveURL('/dashboard');
  await expect(page.locator('h1')).toContainText('Welcome, Alice');
});

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Other Important Test Types