Puppeteer Visual Testing

Setup

TestingBot added a new page.evaluate command which can be used in your Puppeteer tests. Simply pass a `testingbot_executor: ${JSON.stringify({action: 'visual.snapshot', arguments: { name: 'uniqueIdentifier' }})}` argument to have TestingBot take and compare the screenshot.

TestingBot will perform a pixel comparison scan, comparing the screenshot of your website with the original golden image (baseline).
If TestingBot detects the number of different pixels to be higher than the supplied threshold, the test will be marked as failed.

const results = await page.evaluate(_ => {}, `testingbot_executor: ${JSON.stringify({action: 'visual.snapshot', arguments: { name: 'uniqueIdentifier' }})}`)

In the example above, the screenshot will be saved as uniqueIdentifier. Any future calls will compare the screenshot with the screenshot that was saved the first time this command was run.

Visual Comparison Response

Every time you run a visual.snapshot command, TestingBot will return back the visual comparison result in less than 2 seconds.
The response will contain the following information:

• Does the screenshot match the baseline?
• What are the number of pixels that are different between the two snapshots?

{
      "match": false,
      "pixelDifference": 341575
}

Please see the example below on how to check whether a visual change was detected:

const visual_response = await page.evaluate(_ => {}, `testingbot_executor: ${JSON.stringify({action: 'visual.snapshot', arguments: { name: 'uniqueIdentifier' }})}`)
const json_response = JSON.parse(visual_response)
const visual_test_passed = json_response['match'] === true

Visual Baseline

To set a new baseline for your snapshots, you can use the following command:

const visual_response = await page.evaluate(_ => {}, `testingbot_executor: ${JSON.stringify({action: 'visual.baseline', arguments: { name: 'uniqueIdentifier' }})}`)

Visual Testing Options

TestingBot offers various options to customize the visual comparison tests. Options can be passed with the visual.snapshot command:

const visualSnapshotJsonCmd = JSON.stringify({
  name: 'testing123',
  options: {
    threshold: 0.3
  }
})

const visual_response = await page.evaluate(_ => {}, `testingbot_executor: ${JSON.stringify({action: 'visual.snapshot', arguments: visualSnapshotJsonCmd })}`)

Option Name	Default Option Value	Description
threshold	0.1	This defines the color difference threshold (from 0 to 1). The smaller the number, the more precise the comparison will be.
antialiasing	true	When this is set to true, TestingBot will not count antialiased pixels to the diff of the snapshot.
ignoreRegions	[]	Regions to ignore, defined in pixel coordinates. Needs to be an array with these objects: [{ "x1": number, "y1": number, "x2": number, "y2": number }]
ignoreSelectors	[]	Pass an array of CSS Selectors to ignore these DOM elements during the visual check. ["body div.test", "#sidebar"]
selector	-	Pass a CSS selector to take a screenshot of this specific element only. If this is not specified, TestingBot will take a screenshot of the viewport. ["body div.test", "#sidebar"]