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    cypress-visual-regression
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    1.7.0 • Public • Published

    Cypress Visual Regression

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    Module for adding visual regression testing to Cypress.

    Getting Started

    Install:

    $ npm install cypress-visual-regression

    Add the following config to your cypress.json file:

    {
      "screenshotsFolder": "./cypress/snapshots/actual",
      "trashAssetsBeforeRuns": true
    }

    Add the plugin to cypress/plugins/index.js:

    const getCompareSnapshotsPlugin = require('cypress-visual-regression/dist/plugin');
    
    module.exports = (on, config) => {
      getCompareSnapshotsPlugin(on, config);
    };

    Add the command to cypress/support/commands.js:

    const compareSnapshotCommand = require('cypress-visual-regression/dist/command');
    
    compareSnapshotCommand();

    Make sure you import commands.js in cypress/support/index.js:

    import './commands'

    TypeScript

    If you're using TypeScript, use files with a .ts extension, as follows:

    cypress/plugins/index.ts

    import type Cypress from 'cypress';
    import getCompareSnapshotsPlugin from 'cypress-visual-regression/dist/plugin';
    
    export default function configurePlugins(
      on: Cypress.PluginEvents,
      config: Cypress.PluginConfigOptions,
    ) {
      getCompareSnapshotsPlugin(on, config);
    }

    cypress/support/commands.ts

    import compareSnapshotCommand from 'cypress-visual-regression/dist/command';
    
    compareSnapshotCommand();

    cypress/tsconfig.json

    {
      "compilerOptions": {
        "types": [
          "cypress",
          "cypress-visual-regression"
        ]
      }
    }
    

    For more info on how to use TypeScript with Cypress, please refer to this document.

    Options

    failSilently is enabled by default. Add the following config to your cypress.json file to see the errors:

    {
      "env": {
        "failSilently": false
      }
    }

    You can also pass default arguments to compareSnapshotCommand():

    const compareSnapshotCommand = require('cypress-visual-regression/dist/command');
    
    compareSnapshotCommand({
      capture: 'fullPage'
    });

    These will be used by default when no parameters are passed to the compareSnapshot command.

    Configure snapshot paths

    You can control where snapshots should be located by setting two environment variables:

    Variable Description
    SNAPSHOT_BASE_DIRECTORY Directory of the base snapshots
    SNAPSHOT_DIFF_DIRECTORY Directory for the snapshot diff

    The actual directory always points to the configured screenshot directory.

    Configure snapshot generation

    You can control if diff images are generated for successful tests by setting the following environment variable:

    Variable Description
    ALWAYS_GENERATE_DIFF Boolean, defaults to true

    To Use

    Add cy.compareSnapshot('home'); in your tests specs whenever you want to test for visual regressions, making sure to replace home with a relevant name. You can also add an optional error threshold: Value can range from 0.00 (no difference) to 1.00 (every pixel is different). So, if you enter an error threshold of 0.51, the test would fail only if > 51% of pixels are different.

    More examples:

    Threshold Fails when
    .25 > 25%
    .30 > 30%
    .50 > 50%
    .75 > 75%

    Sample:

    it('should display the login page correctly', () => {
      cy.visit('/03.html');
      cy.get('H1').contains('Login');
      cy.compareSnapshot('login', 0.0);
      cy.compareSnapshot('login', 0.1);
    });

    You can target a single HTML element as well:

    cy.get('#my-header').compareSnapshot('just-header')

    You can pass arguments as an object to cy.screenshot(), rather than just an error threshold, as well:

    it('should display the login page correctly', () => {
      cy.visit('/03.html');
      cy.compareSnapshot('login', {
        capture: 'fullPage',
        errorThreshold: 0.1
      });
    });

    Looking for more examples? Review docker/cypress/integration/main.spec.js.

    Take the base images:

    $ ./node_modules/.bin/cypress run --env type=base --config screenshotsFolder=cypress/snapshots/base,testFiles=\"**/*regression-tests.js\"
    
    # use comma separated format for multiple config commands
    $ ./node_modules/.bin/cypress run \
      --env type=base \
      --config screenshotsFolder=cypress/snapshots/base,testFiles=\"**/*regression-tests.js\"

    Find regressions:

    $ ./node_modules/.bin/cypress run --env type=actual

    Example

    example

    Tips & Tricks

    Ignore some elements

    Following function creates a command that allows you to hide elements of the page based on their className:

    /**
     * To be called after you setup the command, in order to add a
     * hook that does stuff before the command is triggered
     */
    function beforeCompareSnapshotCommand(
      /** Element you want to ignore */
      ignoredElementsQuerySelector: string,
      /** Main app element (if you want for the page to be loaded before triggering the command) */
      appContentQuerySelector: string = "body"
    ) {
      Cypress.Commands.overwrite("compareSnapshot", (originalFn, ...args) => {
        return cy
          // wait for content to be ready 
          .get(appContentQuerySelector)
          // hide ignored elements
          .then($app => {
            return new Cypress.Promise((resolve, reject) => {
              setTimeout(() => {
                $app.find(ignoredElementsQuerySelector).css("visibility", "hidden");
                resolve();
                // add a very small delay to wait for the elements to be there, but you should
                // make sure your test already handles this
              }, 300);
            });
          })
          .then(() => {
            return originalFn(...args);
          });
      });
    }
    
    module.exports = beforeCompareSnapshotCommand;

    You may then use this function like below:

    const compareSnapshotCommand = require("cypress-visual-regression/dist/command");
    const beforeCompareSnapshotCommand = require("./commands/beforeCompareSnapshots");
    compareSnapshotCommand({
      errorThreshold: 0.1
    });
    // add a before hook to compareSnapshot (this must be called AFTER compareSnapshotCommand() so the command can be overriden)
    beforeCompareSnapshotCommand(
      ".chromatic-ignore,[data-chromatic='ignore']",
      "._app-content"
    );

    In this example, we ignore the elements that are also ignored by 3rd party tool Chromatic.

    Install

    npm i cypress-visual-regression

    DownloadsWeekly Downloads

    20,600

    Version

    1.7.0

    License

    MIT

    Unpacked Size

    21.9 kB

    Total Files

    10

    Last publish

    Collaborators

    • mjhea0