Web Tester Skill | Agent Skills

Web Tester

Browser-based frontend testing with Playwright. Test user flows, validate UI behavior, and detect visual regressions.

Features

Browser automation - Navigate, click, fill forms, take screenshots
Assertions - Collect all test results, report failures at end
Visual diff - Compare screenshots against baselines with perceptual diff
Dev server detection - Auto-detect running local servers

Setup (First Time)

cd $SKILL_DIR && npm run setup

This installs Playwright and Chromium. Only needed once.

Quick Start

1. Detect dev servers

cd $SKILL_DIR && node -e "require('./lib/helpers').detectDevServers().then(s => console.log(JSON.stringify(s)))"

2. Write test to /tmp

// /tmp/test-homepage.js
const { chromium } = require('playwright');
const helpers = require('./lib/helpers');

(async () => {
  const browser = await chromium.launch({ headless: false });
  const context = await helpers.createContext(browser);
  const page = await context.newPage();

  // Create test with assertions
  const test = helpers.createTest('Homepage Test');

  await page.goto('http://localhost:3000');
  
  test.assert(await page.title() !== '', 'Page has title');
  await test.assertVisible(page, 'nav', 'Navigation is visible');
  await test.assertText(page, 'h1', 'Welcome', 'Hero heading contains Welcome');

  // Visual regression check
  await helpers.compareScreenshot(page, 'homepage');

  await test.finish();
  await browser.close();
})();

3. Execute

cd $SKILL_DIR && node run.js /tmp/test-homepage.js

Assertions API

Create a test to collect assertions:

const test = helpers.createTest('My Test');

// Basic assertion
test.assert(condition, 'Description');

// Element visibility
await test.assertVisible(page, 'selector', 'Description');

// Text content
await test.assertText(page, 'selector', 'expected text', 'Description');

// URL check
await test.assertUrl(page, '/dashboard', 'Description');

// Element count
await test.assertCount(page, '.item', 5, 'Description');

// Attribute check
await test.assertAttribute(page, 'input', 'type', 'email', 'Description');

// Finish and save results
await test.finish();

Results are saved to /tmp/test-results.json.

View results

cd $SKILL_DIR && node run.js --show-results

Clear results

cd $SKILL_DIR && node run.js --clear-results

Visual Regression API

Compare screenshots against baselines:

await helpers.compareScreenshot(page, 'screenshot-name', {
  threshold: 0.5,              // Diff threshold % (default: 0.5)
  baselineDir: './baselines',  // Baseline folder (default: ./visual-baselines)
  fullPage: true               // Full page screenshot (default: true)
});

Baseline workflow

First run - Creates baseline, marks as "pending approval"
Subsequent runs - Compares against baseline
If different - Saves .current.png and .diff.png for review

Manage baselines

# List all baselines and their status
cd $SKILL_DIR && node run.js --list-baselines

# Approve all pending baselines (with confirmation)
cd $SKILL_DIR && node run.js --approve-baselines

# Approve specific baseline
cd $SKILL_DIR && node run.js --approve-baseline homepage

# Reject baseline (keep old, delete current/diff)
cd $SKILL_DIR && node run.js --reject-baseline homepage

Common Patterns

Test login flow

// /tmp/test-login.js
const { chromium } = require('playwright');
const helpers = require('./lib/helpers');

(async () => {
  const browser = await chromium.launch({ headless: false });
  const page = await browser.newPage();
  const test = helpers.createTest('Login Flow');

  await page.goto('http://localhost:3000/login');

  await helpers.safeType(page, 'input[name="email"]', 'test@example.com');
  await helpers.safeType(page, 'input[name="password"]', 'password123');
  await helpers.safeClick(page, 'button[type="submit"]');

  await page.waitForURL('**/dashboard');
  await test.assertUrl(page, '/dashboard', 'Redirected to dashboard');
  await test.assertVisible(page, '.user-menu', 'User menu visible');

  await test.finish();
  await browser.close();
})();

Test responsive design

// /tmp/test-responsive.js
const { chromium } = require('playwright');
const helpers = require('./lib/helpers');

(async () => {
  const browser = await chromium.launch({ headless: false });
  const test = helpers.createTest('Responsive Design');

  const viewports = [
    { name: 'desktop', width: 1920, height: 1080 },
    { name: 'tablet', width: 768, height: 1024 },
    { name: 'mobile', width: 375, height: 667 }
  ];

  for (const vp of viewports) {
    const context = await browser.newContext({ viewport: vp });
    const page = await context.newPage();

    await page.goto('http://localhost:3000');
    await helpers.compareScreenshot(page, `homepage-${vp.name}`);
    
    await test.assertVisible(page, 'nav', `Nav visible on ${vp.name}`);
    await context.close();
  }

  await test.finish();
  await browser.close();
})();

Test form validation

// /tmp/test-form.js
const { chromium } = require('playwright');
const helpers = require('./lib/helpers');

(async () => {
  const browser = await chromium.launch({ headless: false });
  const page = await browser.newPage();
  const test = helpers.createTest('Form Validation');

  await page.goto('http://localhost:3000/contact');

  // Submit empty form
  await helpers.safeClick(page, 'button[type="submit"]');
  await test.assertVisible(page, '.error-message', 'Shows error for empty form');

  // Fill and submit
  await helpers.safeType(page, 'input[name="email"]', 'test@example.com');
  await helpers.safeType(page, 'textarea[name="message"]', 'Hello');
  await helpers.safeClick(page, 'button[type="submit"]');

  await test.assertVisible(page, '.success-message', 'Shows success message');

  await test.finish();
  await browser.close();
})();

Helper Functions

const helpers = require('./lib/helpers');

// Browser setup
await helpers.launchBrowser('chromium', { headless: false });
await helpers.createContext(browser, { viewport: { width: 1920, height: 1080 } });
await helpers.createPage(context);

// Dev server detection
const servers = await helpers.detectDevServers();

// Safe interactions (with retry)
await helpers.safeClick(page, 'button', { retries: 3 });
await helpers.safeType(page, 'input', 'text', { clear: true });

// Page utilities
await helpers.waitForPageReady(page, { waitUntil: 'networkidle' });
await helpers.takeScreenshot(page, 'my-screenshot');
await helpers.handleCookieBanner(page);
await helpers.scrollPage(page, 'bottom');

// Data extraction
const texts = await helpers.extractTexts(page, '.list-item');
const tableData = await helpers.extractTableData(page, 'table');

Inline Execution

For quick tests, run inline code:

cd $SKILL_DIR && node run.js "
const browser = await chromium.launch({ headless: false });
const page = await browser.newPage();
await page.goto('http://localhost:3000');
console.log('Title:', await page.title());
await takeScreenshot(page, 'quick-check');
await browser.close();
"

Environment Variables

| Variable | Description | |----------|-------------| | VISUAL_BASELINE_DIR | Baseline directory (default: ./visual-baselines) | | HEADLESS | Run browser headless if true (default: false) | | SLOW_MO | Slow down actions by ms | | PW_HEADER_NAME + PW_HEADER_VALUE | Add custom HTTP header | | PW_EXTRA_HEADERS | JSON object of extra headers |

CLI Reference

# Execute test file
node run.js /tmp/test.js

# Execute inline code
node run.js "await page.goto('...')"

# Baseline management
node run.js --list-baselines
node run.js --approve-baselines
node run.js --approve-baseline <name>
node run.js --reject-baseline <name>

# Results management
node run.js --show-results
node run.js --clear-results

# Help
node run.js --help

Tips

Always detect servers first for localhost testing
Write tests to /tmp to avoid cluttering projects
Use headless: false by default for easier debugging
Visual baselines need human approval before becoming authoritative
Assertions continue on failure - all results reported at end

Agent Skills: Web Tester

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