Principle:Getgauge Taiko Page Screenshot
| Knowledge Sources | |
|---|---|
| Domains | Browser_Automation, Testing, Debugging |
| Last Updated | 2026-02-12 00:00 GMT |
Overview
Technique for capturing visual snapshots of browser pages or specific elements for debugging, documentation, or failure analysis.
Description
Screenshot capture creates a bitmap image of the current browser viewport, a specific element, or the full scrollable page. This is essential for visual regression testing, debugging test failures, and generating test reports with visual evidence.
Screenshots are commonly captured on test failure to provide visual context for what went wrong. When a test fails, the screenshot shows the exact state of the page at the moment of failure, including error messages, unexpected layouts, or missing elements that caused the assertion to fail.
The capture uses the browser's built-in rendering engine to produce accurate representations of the page as rendered, including CSS styling, JavaScript-rendered content, and dynamic layouts. This means the screenshot reflects exactly what a real user would see, including web fonts, animations frozen at their current frame, and responsive layout adjustments.
Usage
Capture screenshots on test failure for debugging -- this is the most common use case and is typically configured as a global test hook. Use full-page screenshots for visual documentation of entire page flows. Capture element-specific screenshots for targeted visual comparison, such as verifying a chart or widget renders correctly. In CI/CD pipelines, screenshots are commonly attached as artifacts to test reports, enabling developers to diagnose failures without reproducing them locally.
Theoretical Basis
Screenshot capture uses the CDP Page.captureScreenshot API with different strategies depending on the capture scope:
- Viewport capture -- Capture the current visible area of the browser window. This is the simplest mode and produces an image matching the browser's viewport dimensions.
- Full page capture -- Query layout metrics to determine the full content dimensions (including content below the fold), then capture with a clip rectangle set to the full content size. This produces an image that may be much taller than the viewport.
- Element capture -- Get the target element's bounding box coordinates via the DOM API, apply optional padding around the element, then capture with a clip rectangle matching the padded bounding box. This isolates a single element from the surrounding page.
The output is base64-encoded PNG data that can be saved to a file on disk or returned as a buffer for programmatic processing. The PNG format is chosen for its lossless compression, ensuring pixel-perfect accuracy for visual comparison workflows.