I’m having trouble with my end-to-end tests using Jasmine and Puppeteer. The weird thing is that my tests work perfectly when I run them with the browser visible, but they break when I switch to headless mode.
I think the issue might be related to how React components are rendering, but I need to figure out how to debug this properly. The official docs suggest running with headless disabled to see what’s happening, but that doesn’t help me since the problem only occurs in headless mode.
Has anyone found a good way to debug Puppeteer scripts when they’re running headless? I really need to see what’s going wrong during execution.
Console output is a lifesaver for headless debugging. Use page.on('console', msg => console.log(msg.text())) and page.on('pageerror', err => console.log(err.message)) to catch client-side errors and logs you’d normally see in devtools. Try adding {slowMo: 250} to your launch config - it slows things down and often exposes race conditions that only happen in headless mode. The --disable-web-security flag works great too when launching headless Chrome, especially if your React app makes cross-origin requests during tests. Security restrictions can act weird between modes and fail silently.
You’re experiencing inconsistent behavior in your end-to-end tests using Jasmine and Puppeteer. The tests pass when run in headed mode (browser visible), but fail in headless mode. This suggests a discrepancy in how your application renders in these two environments. The problem likely stems from timing issues or rendering differences between headed and headless modes, and you need effective ways to debug this in a headless context.
Understanding the “Why” (The Root Cause):
The core issue is likely related to differences in the browser’s rendering environment between headed and headless modes. Headed mode utilizes the operating system’s graphics processing unit (GPU), leading to faster rendering and potentially masking timing-related issues. Headless mode, lacking a GUI, might render more slowly, expose asynchronous race conditions in your React components, or create subtle differences in how CSS is applied. This can cause test failures that don’t appear in headed mode. Without the visual feedback of a browser window, debugging headless Puppeteer scripts can be significantly more challenging.
Step-by-Step Guide:
Capture Headless Execution Evidence: The most crucial step is gathering information about what’s happening during the headless execution to pinpoint the failure. Use Puppeteer’s built-in tools to document the problematic moment:
Screenshots: Take screenshots at critical points in your tests, especially just before and after the suspected failure. This will visually reveal any rendering differences. Use await page.screenshot({path: 'screenshot.png'}); at key points in your test suite.
DOM Snapshots: Capture the DOM state at various points using await page.content(); and save it to a file or console log it. This shows the exact HTML structure Puppeteer sees, identifying any structural differences from what you see in headed mode.
Console Logging: Utilize page.on('console', msg => console.log(msg.text())) to catch any client-side errors or log messages that might help indicate the root cause of the failure. Client-side errors frequently go unnoticed in headless mode.
Increase Wait Times: Headless mode executes faster than headed mode. Increase the waiting period between actions in your tests to accommodate any potential rendering delays. You can use await page.waitForTimeout(milliseconds); or await page.waitForSelector(selector, options); to wait for specific elements before interacting with them.
Examine Viewport Size: Headless mode uses a smaller default viewport than headed mode (typically 800x600). Differences in viewport size can drastically impact responsive design elements. Before each test, explicitly set the viewport to your expected dimensions: await page.setViewport({ width: 1920, height: 1080 });.
Disable Security Restrictions (Cautiously): In some cases, security restrictions might affect rendering differently in headless mode. Only for debugging purposes, and never for production, you can try temporarily launching Puppeteer with --disable-web-security. This bypasses same-origin policies and cross-origin resource sharing restrictions, which could potentially mask unexpected errors. Remember to remove this option from your final launch settings.
Analyze Network Requests: If your application relies on network calls, examine the network requests (using your browser’s developer tools in headed mode) and compare them with the network requests during headless execution (you can log them using Puppeteer’s page.on('request', request => { ... });). Any differences could highlight inconsistencies in resource loading.
Run Tests in Slow Motion (Debugging Only): While not a permanent solution, adding { slowMo: 250 } to your puppeteer.launch() options drastically slows down Puppeteer’s actions, making it easier to identify race conditions. Use this exclusively for debugging; remove it before final testing.
Common Pitfalls & What to Check Next:
Asynchronous Operations: Pay close attention to the asynchronous nature of Puppeteer and React. Ensure all promises resolve before moving to the next step in your tests. Use await liberally.
React Component Lifecycle: React components might not fully render before Puppeteer attempts to interact with them. Use page.waitForSelector() to wait explicitly for elements to appear in the DOM.
CSS Selectors: Double-check your CSS selectors to ensure they accurately target the elements in your React components. Incorrect selectors frequently cause failures that only appear in headless mode due to slightly different rendering.
Still running into issues? Share your (sanitized) config files, the exact command you ran, and any other relevant details. The community is here to help!
check your viewport size - headless defaults to 800x600 and screws up responsive components. try page.setViewport({width: 1920, height: 1080}) before navigating. also watch for timing issues since headless runs faster than headed mode, so elements might not be loaded when u expect.
Understanding the “Why” (The Root Cause):
Step-by-Step Guide:
Common Pitfalls & What to Check Next:
Still running into issues? Share your (sanitized) config files, the exact command you ran, and any other relevant details. The community is here to help!