Web Application Testing Skill

Version: 1.1.0 Category: Development Last Updated: 2026-01-02

Overview

This toolkit enables testing local web applications using Playwright with Python for frontend verification, UI debugging, screenshot capture, and browser automation.

Quick Start

# Install dependencies
pip install playwright pytest requests
playwright install chromium

from playwright.sync_api import sync_playwright

with sync_playwright() as p:
    browser = p.chromium.launch(headless=True)
    page = browser.new_page()
    page.goto("http://localhost:3000")

    # Take screenshot
    page.screenshot(path="screenshot.png")

    # Get page content
    content = page.content()
    print(content)

    browser.close()

When to Use

• Verifying frontend functionality after code changes
• Debugging UI behavior and layout issues
• Capturing screenshots for documentation
• Viewing browser console logs for errors
• Automating repetitive web interactions
• End-to-end testing of web applications
• Validating form submissions and user flows

Decision Tree

Static HTML

1. Read files directly to find selectors
2. Then automate with Playwright

Dynamic Webapps

1. Check if server runs
2. If not, start with helper script
3. Perform reconnaissance (screenshots/DOM)
4. Then automate

Running Servers

1. Perform reconnaissance first
2. Take screenshots
3. Inspect DOM
4. Then automate

Core Patterns

Wait for Dynamic Content

from playwright.sync_api import sync_playwright

with sync_playwright() as p:
    browser = p.chromium.launch()
    page = browser.new_page()
    page.goto("http://localhost:3000")

    # CRITICAL: Wait for JS to execute
    page.wait_for_load_state("networkidle")

    # Now safe to interact
    content = page.content()
    browser.close()

Element Selection

By Text:

page.get_by_text("Submit").click()
page.get_by_text("Welcome", exact=False).wait_for()

By Role:

page.get_by_role("button", name="Submit").click()
page.get_by_role("textbox", name="Email").fill("test@example.com")
page.get_by_role("link", name="Home").click()

By CSS Selector:

page.locator(".btn-primary").click()
page.locator("#email-input").fill("test@example.com")
page.locator("[data-testid='submit']").click()

By ID:

page.locator("#submit-button").click()

Form Interaction

# Fill form
page.locator("#username").fill("testuser")
page.locator("#password").fill("password123")
page.locator("#remember").check()
page.get_by_role("button", name="Login").click()

# Wait for navigation
page.wait_for_url("**/dashboard")

Screenshots

# Full page
page.screenshot(path="full.png", full_page=True)

# Element only
page.locator(".main-content").screenshot(path="element.png")

# Viewport only
page.screenshot(path="viewport.png")

Console Logs

# Capture console output
console_messages = []

def handle_console(msg):
    console_messages.append({
        "type": msg.type,
        "text": msg.text
    })

page.on("console", handle_console)
page.goto("http://localhost:3000")

# Print captured logs
for msg in console_messages:
    print(f"[{msg['type']}] {msg['text']}")

Network Monitoring

# Capture requests
requests = []

def handle_request(request):
    requests.append({
        "url": request.url,
        "method": request.method
    })

page.on("request", handle_request)
page.goto("http://localhost:3000")

# Print captured requests
for req in requests:
    print(f"{req['method']} {req['url']}")

Server Management

Start Server Before Testing

import subprocess
import time
from playwright.sync_api import sync_playwright

# Start server
server = subprocess.Popen(
    ["npm", "run", "dev"],
    stdout=subprocess.PIPE,
    stderr=subprocess.PIPE
)

# Wait for server to start
time.sleep(3)

try:
    with sync_playwright() as p:
        browser = p.chromium.launch()
        page = browser.new_page()
        page.goto("http://localhost:3000")
        # ... test code ...
        browser.close()
finally:
    server.terminate()

Check Server Status

import requests

def is_server_running(url="http://localhost:3000"):
    try:
        response = requests.get(url, timeout=2)
        return response.status_code == 200
    except:
        return False

Testing Patterns

Assertion Examples

from playwright.sync_api import expect

# Text content
expect(page.locator("h1")).to_have_text("Welcome")

# Visibility
expect(page.locator(".modal")).to_be_visible()
expect(page.locator(".loading")).to_be_hidden()

# Input values
expect(page.locator("#email")).to_have_value("test@example.com")

# Count
expect(page.locator(".item")).to_have_count(5)

# URL
expect(page).to_have_url("http://localhost:3000/dashboard")

Test Structure

import pytest
from playwright.sync_api import sync_playwright

@pytest.fixture(scope="session")
def browser():
    with sync_playwright() as p:
        browser = p.chromium.launch()
        yield browser
        browser.close()

@pytest.fixture
def page(browser):
    page = browser.new_page()
    yield page
    page.close()

def test_homepage(page):
    page.goto("http://localhost:3000")
    assert page.title() == "My App"

def test_login(page):
    page.goto("http://localhost:3000/login")
    page.fill("#username", "testuser")
    page.fill("#password", "password")
    page.click("button[type='submit']")
    page.wait_for_url("**/dashboard")

Usage Examples

Example 1: Screenshot Comparison Testing

from playwright.sync_api import sync_playwright
from pathlib import Path

def capture_page_state(url: str, output_dir: str):
    """Capture full page screenshot and HTML content."""
    output = Path(output_dir)
    output.mkdir(parents=True, exist_ok=True)

    with sync_playwright() as p:
        browser = p.chromium.launch()
        page = browser.new_page()
        page.goto(url)
        page.wait_for_load_state("networkidle")

        # Screenshot
        page.screenshot(path=str(output / "screenshot.png"), full_page=True)

        # HTML content
        (output / "content.html").write_text(page.content())

        browser.close()

    return output

# Usage
capture_page_state("http://localhost:3000", "tests/snapshots/")

Example 2: Form Automation

def submit_contact_form(page, name, email, message):
    """Submit a contact form and verify success."""
    page.goto("http://localhost:3000/contact")

    # Fill form fields
    page.fill("[name='name']", name)
    page.fill("[name='email']", email)
    page.fill("[name='message']", message)

    # Submit
    page.click("button[type='submit']")

    # Wait for success message
    page.wait_for_selector(".success-message")

    return page.locator(".success-message").text_content()

Example 3: API Response Verification

def verify_api_call(page, endpoint_pattern):
    """Intercept and verify API calls."""
    api_response = None

    def handle_response(response):
        nonlocal api_response
        if endpoint_pattern in response.url:
            api_response = response.json()

    page.on("response", handle_response)
    page.goto("http://localhost:3000/dashboard")
    page.wait_for_load_state("networkidle")

    return api_response

Debugging

Slow Motion

browser = p.chromium.launch(slow_mo=500)  # 500ms delay between actions

Headed Mode

browser = p.chromium.launch(headless=False)  # See the browser

Pause Execution

page.pause()  # Opens Playwright Inspector

Trace Recording

context = browser.new_context()
context.tracing.start(screenshots=True, snapshots=True)

page = context.new_page()
# ... test code ...

context.tracing.stop(path="trace.zip")
# View with: playwright show-trace trace.zip

Best Practices

Do

1. Wait appropriately using networkidle for dynamic content
2. Select elements by text, role, or data-testid over CSS
3. Handle async operations with proper waits
4. Clean up browsers and pages after tests
5. Use fixtures for browser instance reuse
6. Capture console logs for debugging

Don't

1. Use arbitrary time.sleep() for waits
2. Rely on fragile CSS selectors
3. Skip error handling in test cleanup
4. Run tests without checking server status
5. Ignore network errors during testing

Error Handling

Common Errors

Error	Cause	Solution
TimeoutError	Element not found in time	Use explicit waits or increase timeout
Page closed	Browser closed prematurely	Check cleanup order in fixtures
Connection refused	Server not running	Start server before tests
Element not visible	Hidden by CSS/JS	Wait for visibility state
Target closed	Navigation during action	Wait for navigation to complete

Debugging Tips

# Increase default timeout
page.set_default_timeout(60000)  # 60 seconds

# Take screenshot on failure
try:
    page.click("#submit")
except Exception as e:
    page.screenshot(path="error_screenshot.png")
    raise

# Print page HTML for debugging
print(page.content())

Execution Checklist

• Playwright and chromium installed
• Server running before tests
• Proper wait states for dynamic content
• Screenshots captured for visual verification
• Console logs monitored for errors
• Network requests validated
• Fixtures clean up browser resources
• Error screenshots captured on failure
• Tests run in both headed and headless modes

Metrics

Metric	Target	Description
Test Duration	<10s per test	Individual test execution time
Flakiness Rate	<2%	Tests passing consistently
Screenshot Match	100%	Visual regression accuracy
Network Coverage	>90%	API endpoints tested

Dependencies

pip install playwright pytest requests
playwright install chromium

Related Skills

• engineering-report-generator - Generate test reports
• data-pipeline-processor - Process test data
• parallel-file-processor - Batch screenshot processing

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Version History

• 1.1.0 (2026-01-02): Upgraded to SKILL_TEMPLATE_v2 format with Quick Start, Usage Examples, Error Handling, Metrics, Execution Checklist
• 1.0.0 (2024-10-15): Initial release with Playwright patterns, server management, debugging tools