When working with web automation and browser tests, Playwright has become a popular choice due to its speed, cross-browser capabilities, and powerful APIs. However, like all code, Playwright scripts can sometimes face unexpected issues that require debugging and troubleshooting. This guide will explore techniques and tools to effectively pinpoint and resolve issues in Playwright scripts written in Python.
1. Understanding Common Playwright Issues
Before jumping into debugging, it is essential to understand the common issues that can arise:
- Timeout Errors: These occur when an operation takes longer than expected.
- Element Not Found: Happens when a script tries to interact with an element not available or loaded.
- Unstable Tests: Flaky tests that pass intermittently can stem from poor test environment conditions or script issues.
2. Enable Built-in Debug Mode
Playwright offers a debug mode to help step through your script execution and inspect the state.
# Use the `PWDEBUG` environment variable
import os
os.environ['PWDEBUG'] = '1'
Launching your Playwright script with this setting will open an inspector window where you can look at various elements, view execution step-by-step, and see network calls.
3. Utilize Console Logs
Console logs are invaluable for tracking the flow of script execution and understanding what's happening at each step.
# Add print statements or use the logging module
print("Test Started")
print("Navigating to page...")
import logging
logging.basicConfig(level=logging.INFO)
logging.info("This info message will appear on logs")
Python's logging module allows more complex logging solutions, setting different levels like DEBUG, INFO, WARNING, etc.
4. Use Browser Context Tracing
Playwright supports tracing, which creates a trace file with DOM snapshots, input events, network requests, and more.
# Browser context tracing usage
from playwright.sync_api import sync_playwright
with sync_playwright() as p:
browser = p.chromium.launch()
context = browser.new_context(permissions=[], viewport={'width': 800, 'height': 600})
# Start tracing before the action
context.tracing.start(screenshots=True, snapshots=True)
page = context.new_page()
page.goto("https://example.com")
# Stop tracing
context.tracing.stop(path = "trace.zip")
This trace file can then be opened using Playwright tools to replay and inspect the recorded session.
5. Screenshot and Video Capture
Sometimes visual logs show what went wrong better than verbose text logs can.
# Taking a screenshot
page.screenshot(path="screenshot.png")
# Recording video of page/test interactions
context = browser.new_context(record_video_dir="./videos/")
Screenshots and video captures can help diagnose UI-related issues especially when the error is related to visual defects or incorrect rendering.
6. Element Handling Troubleshooting
Issues where elements are not interactable can often be resolved by:
- Checking Locators: Ensure the locators are correctly defined and attempt to wait for elements to appear.
- Using Wait Functions: Use built-in functions to wait for elements' readiness.
# Example of waiting for an element
page.wait_for_selector("#submit-button")
page.locator("#submit-button").click()
7. Reviewing Browser Console Logs
Capturing errors and warnings from the browser's console can provide insight into issues not obvious at the script level.
def handle_console_msg(msg):
print(f'Console Message: {msg.text}')
page.on('console', handle_console_msg)
page.goto("https://example.com")
Keep an eye out for any red flags that details browser runtime issues or JavaScript errors.
Conclusion
Debugging Playwright scripts in Python requires a mix of tools and techniques, from utilizing built-in features like tracing and debugging modes, to using best practices for log assertions. With a methodical approach, it becomes manageable to diagnose and fix Playwright script issues effectively. The key is to methodically identify what went awry and use appropriate strategies to solve each issue systematically.
