getVisualDifferences

getVisualDifferences(imageName[, options])

Compares the specified current image with an expected base image. Returns a Promise that resolves to an object with comparison results, but does not run any assertions. This method can be used, if you want to only inspect the differences between images.

For the test, there must be an image with the specified name inside the dirActual folder (usually output/) and dirExpected folder (usually screenshots/base/). Both images can be generated using the takeScreenshot() method.

Tip: The method signature and comparison behavior is identical to checkVisualDifferences

Parameters

imageName

Name of an existing image. The .png extension is optional. An image with that filename must exist inside the dirActual folder, and the dirExpected folder.

options

Optional. Custom comparison options for this check. If no options are defined, the defaults from the helper configuration are used.

Here is a list of all options.

Returns

Always returns a Promise that resolves to the comparison results. The results object contains the following attributes:

• match (boolean) - Whether the differences are within the allowed tolerance level.
• diffImage (string) - Filename of the diff-file.
• diffPixels (int) - Absolute count of different pixels.
• totalPixels (int) - Absolute count of all pixels inside the image.
• relevantPixels (int) - Absolute count of pixels, that are not ignored and inside the bounds-area.
• difference (float) - Relative difference between both images. The percentage is calculated from the diffPixels and relevantPixels values.

Samples

const res = await I.getVisualDifferences("dashboard");

if (res.match) {
    // Identical enough. Difference is 0%
    I.say(`Identical enough. Difference is ${res.difference}%`);
} else {
    // Too different. Difference is 1.2345% - review Diff_dashboard.png for details!
    I.say(`Too different. Difference is ${res.difference}% - review ${res.diffImage} for details!`);
}