Webapp Testing

Web Application Testing

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

Available helper scripts:

• scripts/with_server.py — manages the server lifecycle (supports multiple servers)

Always run scripts with --help first to see usage. Do NOT read the source until you have tried running the script and discovered that a custom solution is absolutely necessary. These scripts can be very large and would otherwise pollute the context window. They are designed to be invoked directly as black-box scripts, not absorbed into context.

Decision tree: choosing an 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 launch 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 the 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 the 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 the discovered selectors

Common pitfall

❌ Do not inspect the DOM before waiting for networkidle on dynamic apps ✅ Do wait with page.wait_for_load_state('networkidle') before inspection

Best practices

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

Reference files

• examples/ — Examples showing common patterns:
  • element_discovery.py — Discovering buttons, links, and input fields on a page
  • static_html_automation.py — Using a file:// URL for local HTML
  • console_logging.py — Capturing console logs during automation