jest-image-snapshot

Jest matcher that performs image comparisons using Blink-diff and behaves just like Jest snapshots do! Very useful for browser visual comparison testing.

Installation:

1. Install:

npm i --save-dev jest-image-snapshot

2. Extend Jest's expect:

  const { toMatchImageSnapshot } = require('jest-image-snapshot');

  expect.extend({ toMatchImageSnapshot });

Usage:

it('should demonstrate this matcher`s usage', () => {
  ...
  expect(image).toMatchImageSnapshot();
});

Given an image (should be either a PNGImage instance or a Buffer instance with PNG data) the toMatchImageSnapshot() matcher will create a __image_snapshots__ directory in the directory the test is in and will store the baseline snapshot image there on the first run.

On subsequent test runs the matcher will compare the image being passed against the stored snapshot.

To update the stored image snapshot run jest with --updateSnapshot or -u argument. All this works the same way as Jest snapshots.

Typically this matcher is used to for visual tests that run on a browser. For example:

  it('should render correctly in browser', async () => {
    // everything above the expect is pseudo-code, obvi
    const browser = await launchChromeHeadless();
    await browser.goToUrl('https://google.com');
    const screenshot = await browser.takeScreenshot();

    expect(screenshot).toMatchImageSnapshot();
    });
  });

Optional configuration:

toMatchImageSnapshot() takes an optional options object where you can provide your own blink-diff configuration parameters and/or a custom snapshot identifier string:

  it('should demonstrate this matcher`s usage with a custom blink-diff config', () => {
    ...
    const blinkDiffConfig = { perceptual: true };
    expect(image).toMatchImageSnapshot({ customDiffConfig: blinkDiffConfig, customSnapshotIdentifier: 'customSnapshotName' });
  });  

Any blink-diff custom configuration can be provided so long as the values for imageAPath, imageA, imageBPath, imageB, or imageOutputPath are not changed as these are used internally.

Contributing

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Please feel free to open pull requests and see CONTRIBUTING.md for commit formatting details.

License

Any contributions made under this project will be governed by the Apache License 2.0.

Code of Conduct

This project adheres to the American Express Community Guidelines. By participating, you are expected to honor these guidelines.