Catch visual regressions in Cypress
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README.md

Cypress Image Snapshot

Cypress Image Snapshot binds jest-image-snapshot's image diffing logic to Cypress.io commands. The goal is to catch visual regressions during integration tests.

See it in action!

Cypress GUI

When using cypress open, errors are displayed in the GUI.

Cypress Image Snapshot in action

Composite Image Diff

When an image diff fails, a composite image is constructed.

Cypress Image Snapshot diff

Test Reporter

When using cypress run and --reporter cypress-image-snapshot/reporter, diffs are output to your terminal.

Cypress Image Snapshot reporter

Installation

Install from npm

npm install --save-dev cypress-image-snapshot

then add the following in your project's <rootDir>/cypress/plugins/index.js:

const {
  addMatchImageSnapshotPlugin,
} = require('cypress-image-snapshot/plugin');

module.exports = (on, config) => {
  addMatchImageSnapshotPlugin(on, config);
};

and in <rootDir>/cypress/support/commands.js add:

import { addMatchImageSnapshotCommand } from 'cypress-image-snapshot/command';

addMatchImageSnapshotCommand(options);

Syntax

// addMatchImageSnapshotPlugin
addMatchImageSnapshotPlugin(on, config);

// addMatchImageSnapshotCommand
addMatchImageSnapshotCommand();
addMatchImageSnapshotCommand(commandName);
addMatchImageSnapshotCommand(options);
addMatchImageSnapshotCommand(commandName, options);

// matchImageSnapshot
.matchImageSnapshot();
.matchImageSnapshot(name);
.matchImageSnapshot(options);
.matchImageSnapshot(name, options);

// ---or---

cy.matchImageSnapshot();
cy.matchImageSnapshot(name);
cy.matchImageSnapshot(options);
cy.matchImageSnapshot(name, options);

Usage

In your tests

describe('Login', () => {
  it('should be publicly accessible', () => {
    cy.visit('/login');

    // snapshot name will be the test title
    cy.matchImageSnapshot();

    // snapshot name will be the name passed in
    cy.matchImageSnapshot('login');

    // options object passed in
    cy.matchImageSnapshot(options);

    // match element snapshot
    cy.get('#login').matchImageSnapshot();
  });
});

Updating snapshots

Run Cypress with --env updateSnapshots=true in order to update the base image files for all of your tests.

Preventing failures

Run Cypress with --env failOnSnapshotDiff=false in order to prevent test failures when an image diff does not pass.

Reporter

Run Cypress with --reporter cypress-image-snapshot/reporter in order to report snapshot diffs in your test results. This can be helpful to use with --env failOnSnapshotDiff=false in order to quickly view all failing snapshots and their diffs.

If you using iTerm2, the reporter will output any image diffs right in your terminal 😎.

Multiple reporters

Similar use case to: https://github.com/cypress-io/cypress-example-docker-circle#spec--xml-reports

If you want to report snapshot diffs as well as generate XML junit reports, you can use mocha-multi-reporters.

npm install --save-dev mocha mocha-multi-reporters mocha-junit-reporter

You'll then want to set up a cypress-reporters.json which may look a little like this:

{
  "reporterEnabled": "spec, mocha-junit-reporter, cypress-image-snapshot/reporter",
  "mochaJunitReporterReporterOptions": {
    "mochaFile": "cypress/results/results-[hash].xml"
  }
}

where reporterEnabled is a comma-separated list of reporters.

You can then run cypress like this:

cypress run --reporter mocha-multi-reporters --reporter-options configFile=cypress-reporters.json

or add the following to your cypress.json

{
  ..., //other options
  "reporter": "mocha-multi-reporters",
  "reporterOptions": {
    "configFile": "cypress-reporters.json"
  }
}

Options

  • customSnapshotsDir : Path to the directory that snapshot images will be written to, defaults to <rootDir>/cypress/snapshots.
  • customDiffDir: Path to the directory that diff images will be written to, defaults to a sibling __diff_output__ directory alongside each snapshot.

Additionally, any options for cy.screenshot() and jest-image-snapshot can be passed in the options argument to addMatchImageSnapshotCommand and cy.matchImageSnapshot(). The local options in cy.matchImageSnapshot() will overwrite the default options set in addMatchImageSnapshot.

For example, the default options we use in <rootDir>/cypress/support/commands.js are:

addMatchImageSnapshotCommand({
  failureThreshold: 0.03, // threshold for entire image
  failureThresholdType: 'percent', // percent of image or number of pixels
  customDiffConfig: { threshold: 0.1 }, // threshold for each pixel
  capture: 'viewport', // capture viewport in screenshot
});

How it works

We really enjoy the diffing workflow of jest-image-snapshot and wanted to have a similar workflow when using Cypress. Because of this, under the hood we use some of jest-image-snapshot's internals and simply bind them to Cypress's commands and plugins APIs.

The workflow of cy.matchImageSnapshot() when running Cypress is:

  1. Take a screenshot with cy.screenshot() named according to the current test.
  2. Check if a saved snapshot exists in <rootDir>/cypress/snapshots and if so diff against that snapshot.
  3. If there is a resulting diff, save it to <rootDir>/cypress/snapshots/__diff_output__.

Cypress Version Requirements

Cypress's screenshot functionality has changed significantly across 3.x.x versions. In order to avoid buggy behavior, please use the following version ranges:

  • cypress-image-snapshot@>=1.0.0 <2.0.0 for cypress@>=3.0.0 <3.0.2
  • cypress-image-snapshot@>2.0.0 for cypress@>3.0.2.