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Web Application Testing

To test local web applications, write native Python Playwright scripts.

Helper Scripts Available:

  • scripts/with_server.py - Manages server lifecycle (supports multiple servers)

Always run scripts with --help first to see usage. DO NOT read the source until you try running the script first and find that a customized solution is abslutely necessary. These scripts can be very large and thus pollute your context window. They exist to be called directly as black-box scripts rather than ingested into your context window.

Decision Tree: Choosing Your Approach

User task → Is it static HTML?
    ├─ Yes → Read HTML file directly to identify selectors
    │         ├─ Success → Write Playwright script using selectors
    │         └─ Fails/Incomplete → Treat as dynamic (below)
    │
    └─ No (dynamic webapp) → Is the server already running?
        ├─ No → Run: python scripts/with_server.py --help
        │        Then use the helper + write simplified Playwright script
        │
        └─ Yes → Reconnaissance-then-action:
            1. Navigate and wait for networkidle
            2. Take screenshot or inspect DOM
            3. Identify selectors from rendered state
            4. Execute actions with discovered selectors

Example: Using with_server.py

To start a server, run --help first, then use the helper:

Single server:

python scripts/with_server.py --server "npm run dev" --port 5173 -- python your_automation.py

Multiple servers (e.g., backend + frontend):

python scripts/with_server.py \
  --server "cd backend && python server.py" --port 3000 \
  --server "cd frontend && npm run dev" --port 5173 \
  -- python your_automation.py

To create an automation script, include only Playwright logic (servers are managed automatically):

from playwright.sync_api import sync_playwright

with sync_playwright() as p:
    browser = p.chromium.launch(headless=True) # Always launch chromium in headless mode
    page = browser.new_page()
    page.goto('http://localhost:5173') # Server already running and ready
    page.wait_for_load_state('networkidle') # CRITICAL: Wait for JS to execute
    # ... your automation logic
    browser.close()

Reconnaissance-Then-Action Pattern

  1. Inspect rendered DOM:

    page.screenshot(path='/tmp/inspect.png', full_page=True)
content = page.content()
page.locator('button').all()

  2. Identify selectors from inspection results

  3. Execute actions using discovered selectors

Common Pitfall

Don't inspect the DOM before waiting for networkidle on dynamic apps Do wait for page.wait_for_load_state('networkidle') before inspection

Best Practices

  • Use bundled scripts as black boxes - To accomplish a task, consider whether one of the scripts available in scripts/ can help. These scripts handle common, complex workflows reliably without cluttering the context window. Use --help to see usage, then invoke directly.
  • Use sync_playwright() for synchronous scripts
  • Always close the browser when done
  • Use descriptive selectors: text=, role=, CSS selectors, or IDs
  • Add appropriate waits: page.wait_for_selector() or page.wait_for_timeout()

Helper Script: with_server.py

Starts one or more servers, waits for them to be ready, runs a command, then cleans up.

#!/usr/bin/env python3
import subprocess
import socket
import time
import sys
import argparse

def is_server_ready(port, timeout=30):
    """Wait for server to be ready by polling the port."""
    start_time = time.time()
    while time.time() - start_time < timeout:
        try:
            with socket.create_connection(('localhost', port), timeout=1):
                return True
        except (socket.error, ConnectionRefusedError):
            time.sleep(0.5)
    return False


def main():
    parser = argparse.ArgumentParser(description='Run command with one or more servers')
    parser.add_argument('--server', action='append', dest='servers', required=True, help='Server command (can be repeated)')
    parser.add_argument('--port', action='append', dest='ports', type=int, required=True, help='Port for each server (must match --server count)')
    parser.add_argument('--timeout', type=int, default=30, help='Timeout in seconds per server (default: 30)')
    parser.add_argument('command', nargs=argparse.REMAINDER, help='Command to run after server(s) ready')

    args = parser.parse_args()

    # Remove the '--' separator if present
    if args.command and args.command[0] == '--':
        args.command = args.command[1:]

    if not args.command:
        print("Error: No command specified to run")
        sys.exit(1)

    # Parse server configurations
    if len(args.servers) != len(args.ports):
        print("Error: Number of --server and --port arguments must match")
        sys.exit(1)

    servers = []
    for cmd, port in zip(args.servers, args.ports):
        servers.append({'cmd': cmd, 'port': port})

    server_processes = []

    try:
        # Start all servers
        for i, server in enumerate(servers):
            print(f"Starting server {i+1}/{len(servers)}: {server['cmd']}")

            # Use shell=True to support commands with cd and &&
            process = subprocess.Popen(
                server['cmd'],
                shell=True,
                stdout=subprocess.PIPE,
                stderr=subprocess.PIPE
            )
            server_processes.append(process)

            # Wait for this server to be ready
            print(f"Waiting for server on port {server['port']}...")
            if not is_server_ready(server['port'], timeout=args.timeout):
                raise RuntimeError(f"Server failed to start on port {server['port']} within {args.timeout}s")

            print(f"Server ready on port {server['port']}")

        print(f"\nAll {len(servers)} server(s) ready")

        # Run the command
        print(f"Running: {' '.join(args.command)}\n")
        result = subprocess.run(args.command)
        sys.exit(result.returncode)

    finally:
        # Clean up all servers
        print(f"\nStopping {len(server_processes)} server(s)...")
        for i, process in enumerate(server_processes):
            try:
                process.terminate()
                process.wait(timeout=5)
            except subprocess.TimeoutExpired:
                process.kill()
                process.wait()
            print(f"Server {i+1} stopped")
        print("All servers stopped")


if __name__ == '__main__':
    main()

Example: Element Discovery

Discovering buttons, links, and inputs on a page:

from playwright.sync_api import sync_playwright

with sync_playwright() as p:
    browser = p.chromium.launch(headless=True)
    page = browser.new_page()

    # Navigate to page and wait for it to fully load
    page.goto('http://localhost:5173')
    page.wait_for_load_state('networkidle')

    # Discover all buttons on the page
    buttons = page.locator('button').all()
    print(f"Found {len(buttons)} buttons:")
    for i, button in enumerate(buttons):
        text = button.inner_text() if button.is_visible() else "[hidden]"
        print(f"  [{i}] {text}")

    # Discover links
    links = page.locator('a[href]').all()
    print(f"\nFound {len(links)} links:")
    for link in links[:5]:  # Show first 5
        text = link.inner_text().strip()
        href = link.get_attribute('href')
        print(f"  - {text} -> {href}")

    # Discover input fields
    inputs = page.locator('input, textarea, select').all()
    print(f"\nFound {len(inputs)} input fields:")
    for input_elem in inputs:
        name = input_elem.get_attribute('name') or input_elem.get_attribute('id') or "[unnamed]"
        input_type = input_elem.get_attribute('type') or 'text'
        print(f"  - {name} ({input_type})")

    # Take screenshot for visual reference
    page.screenshot(path='/tmp/page_discovery.png', full_page=True)
    print("\nScreenshot saved to /tmp/page_discovery.png")

    browser.close()

Example: Static HTML Automation

Using file:// URLs for local HTML files:

from playwright.sync_api import sync_playwright
import os

html_file_path = os.path.abspath('path/to/your/file.html')
file_url = f'file://{html_file_path}'

with sync_playwright() as p:
    browser = p.chromium.launch(headless=True)
    page = browser.new_page(viewport={'width': 1920, 'height': 1080})

    # Navigate to local HTML file
    page.goto(file_url)

    # Take screenshot
    page.screenshot(path='/tmp/static_page.png', full_page=True)

    # Interact with elements
    page.click('text=Click Me')
    page.fill('#name', 'John Doe')
    page.fill('#email', '[email protected]')

    # Submit form
    page.click('button[type="submit"]')
    page.wait_for_timeout(500)

    # Take final screenshot
    page.screenshot(path='/tmp/after_submit.png', full_page=True)

    browser.close()

Example: Console Log Capture

Capturing console logs during browser automation:

from playwright.sync_api import sync_playwright

url = 'http://localhost:5173'  # Replace with your URL

console_logs = []

with sync_playwright() as p:
    browser = p.chromium.launch(headless=True)
    page = browser.new_page(viewport={'width': 1920, 'height': 1080})

    # Set up console log capture
    def handle_console_message(msg):
        console_logs.append(f"[{msg.type}] {msg.text}")
        print(f"Console: [{msg.type}] {msg.text}")

    page.on("console", handle_console_message)

    # Navigate to page
    page.goto(url)
    page.wait_for_load_state('networkidle')

    # Interact with the page (triggers console logs)
    page.click('text=Dashboard')
    page.wait_for_timeout(1000)

    browser.close()

# Save console logs to file
with open('/tmp/console.log', 'w') as f:
    f.write('\n'.join(console_logs))

print(f"\nCaptured {len(console_logs)} console messages")