# Testing That a Canvas Diagram Actually Painted Pixels

DevFeed: [Testing That a Canvas Diagram Actually Painted Pixels](<https://devfeed.tech/articles/testing-that-a-canvas-diagram-actually-painted-pixels-34098.md>)

Original publisher: [Read original article](<https://philipptheserver.com/posts/canvas-pixel-testing/>)

Author: Philipp Lehmann (philipp.lehmann@gruppe.ai)

Published: 2026-07-21T07:00:00Z

Content type: tutorial

Language: en

Sources: [Philipp Lehmann](<https://devfeed.tech/sources/philipp-lehmann.md>)

Topics: [Canvas](<https://devfeed.tech/topics/canvas.md>), [Testing](<https://devfeed.tech/topics/testing.md>), [Playwright](<https://devfeed.tech/topics/playwright.md>), [Document Object Model (DOM)](<https://devfeed.tech/topics/dom.md>), [browser](<https://devfeed.tech/topics/browser.md>)

Tags: [browser](<https://devfeed.tech/tags/browser.md>), [canvas](<https://devfeed.tech/tags/canvas.md>), [frontend](<https://devfeed.tech/tags/frontend.md>), [html5](<https://devfeed.tech/tags/html5.md>), [playwright](<https://devfeed.tech/tags/playwright.md>), [testing](<https://devfeed.tech/tags/testing.md>)

## AI overview

This tutorial explains why DOM-based tests can pass even when an HTML5 canvas renders nothing. Because canvas pixels are not represented in the DOM and jsdom does not provide real canvas rendering, it recommends using Playwright with a real browser and checking pixel data with getImageData.

## Source excerpt

getImageData in Playwright to assert a canvas actually drew pixels, since jsdom has no canvas renderer and DOM assertions pass on a blank canvas.