Chapter 17: AI-Assisted Testing

Test Generation

Agents excel at generating comprehensive test suites from implementations. On real teams this is how coverage moves from under 10% to 40% with no dedicated QA team - the agent writes the unit and integration tests, humans review them, and the suite runs as a CI gate.

// Prompt: "Generate Vitest tests for this function"

// userService.js
async function createUser(userData) {
  if (!userData.email) throw new Error('Email required');
  if (!validateEmail(userData.email)) throw new Error('Invalid email');

  const existing = await User.findOne({ email: userData.email });
  if (existing) throw new Error('Email already exists');

  return await User.create(userData);
}

// AI generates: userService.test.js
import { describe, it, expect, beforeEach } from 'vitest';

describe('createUser', () => {
  beforeEach(async () => {
    await User.deleteMany({});
  });

  it('creates a user with valid data', async () => {
    const user = await createUser({ email: '[email protected]', name: 'Test' });
    expect(user.email).toBe('[email protected]');
  });

  it('throws if email missing', async () => {
    await expect(createUser({})).rejects.toThrow('Email required');
  });

  it('throws if email invalid', async () => {
    await expect(createUser({ email: 'invalid' })).rejects.toThrow('Invalid email');
  });

  it('throws if email already exists', async () => {
    await User.create({ email: '[email protected]' });
    await expect(createUser({ email: '[email protected]' }))
      .rejects.toThrow('Email already exists');
  });
});

UI Regression with Playwright

Agent-generated unit tests plus Playwright-driven UI regression suites are the combination that lets teams ship fast and ship quality - not one or the other. Agents can author Playwright specs from a user story and keep them current as the UI evolves, and product teams can be cross-trained to own smoke and release-regression suites.

import { test, expect } from '@playwright/test';

test('user registration flow', async ({ page }) => {
  await page.goto('/register');
  await page.getByLabel('Email').fill('[email protected]');
  await page.getByLabel('Password').fill('SecurePass123!');
  await page.getByRole('button', { name: 'Sign Up' }).click();
  await expect(page.getByText('Welcome, John')).toBeVisible();
});

Tests as the Verification Layer

In an agentic SDLC, the test suite is not just quality assurance - it is the verification layer that makes autonomous work trustworthy. When an async agent returns a PR, the tests and evals are what confirm the work is actually done. A release that lands on time but does not work is not a win - it is a cleanup project handed to next sprint. Tests are how you avoid handing that project to yourself.