Cypress Visual Regression
Module for adding visual regression testing to Cypress.
Installation
npm install cypress-visual-regression
Configuration
JavaScript
Configure the visual regression plugin and environment variables in your cypress.config.js file like:
const { defineConfig } = require("cypress")
const { configureVisualRegression } = require('cypress-visual-regression')
module.exports = defineConfig({
e2e: {
env: {
visualRegression: {
type: 'regression'
}
},
screenshotsFolder: './cypress/snapshots/actual',
setupNodeEvents(on, config) {
configureVisualRegression(on)
}
}
})
Pay attention to the type
option. Use 'base' to generate baseline images, and 'regression' to compare current
screenshot to the base screenshot
In your support file cypress/support/e2e.js add the following:
const { addCompareSnapshotCommand } = require('cypress-visual-regression/dist/command')
addCompareSnapshotCommand()
TypeScript
If you're using TypeScript, use files with a .ts
extension, as follows:
cypress.config.ts
import { defineConfig } from 'cypress'
import { configureVisualRegression } from 'cypress-visual-regression/dist/plugin'
export default defineConfig({
e2e: {
env: {
visualRegression: {
type: 'regression'
}
},
screenshotsFolder: './cypress/snapshots/actual',
setupNodeEvents(on, config) {
configureVisualRegression(on)
},
},
})
cypress/support/e2e.ts
import { addCompareSnapshotCommand } from 'cypress-visual-regression/dist/command'
addCompareSnapshotCommand()
cypress/tsconfig.json
{
"compilerOptions": {
"esModuleInterop": true,
"types": [
"cypress",
"cypress-visual-regression"
]
}
}
For more info on how to use TypeScript with Cypress, please refer to this document.
Plugin options
All options can be configured within visualRegression
under env
variable inside cypress.config.js
file, like this:
e2e: {
screenshotsFolder: './cypress/snapshots/actual',
env: {
visualRegression: {
type: 'regression',
baseDirectory: 'cypress/snapshot/base',
diffDirectory: 'cypress/snapshot/diff',
generateDiff: 'always',
failSilently: true
}
}
}
Variable | Default | Description |
---|---|---|
type | / | Either 'regression' or 'base'. Base will override any existing base images with new screenshots. Regression will compare the base to the current screenshot. |
baseDirectory | 'cypress/snapshot/base' | Path to the directory where the base snapshots will be stored. |
diffDirectory | 'cypress/snapshot/diff' | Path to the directory where the generated image differences will be stored. |
generateDiff | 'fail' | Either 'fail', 'never' or 'always'. Determines if and when image differences are generated. |
failSilently | false | Used to decide if any error found in regression should be thrown or returned as part of the result. |
You can also pass default cypress screenshot arguments to addCompareSnapshotCommand()
, like this:
const addCompareSnapshotCommand = require('cypress-visual-regression/dist/command')
addCompareSnapshotCommand({
capture: 'fullPage'
})
How To Use
> syntax
cy.compareSnapshot(name)
cy.compareSnapshot(name, errorThreshold)
cy.compareSnapshot(name, options)
> arguments
Arguments | Default | Description |
---|---|---|
name | / | Represents the name of the base snapshot file that the actual screenshot will be compared with. |
errorThreshold | 0 | Threshold under which any image difference will be considered as failed test. Represented in percentages. |
options | {} | Used to provide additional cypress screenshot options as well as failSilently and errorThreshold values. |
> examples
cy.compareSnapshot('homePage') // will compare actual screenshot to current and fail if there's any difference in the images
cy.get('h1').compareSnapshot('homePage', 0.2) // will compare only the image of h1 element and fail only if the percentage of pixels that are different is bigger than 0.2%
cy.compareSnapshot('homePage', {errorThreshold: 1, failSilently: true}).then(comparisonResults => {
console.log(comparisonResults.mismatchedPixels) // will print the number of mismatched pixels
console.log(comparisonResults.percentage) // will print the percentage of mismatched pixels
console.log(comparisonResults.error) // will print the visual regression error message (if any)
})
Looking for more examples? See cypress/e2e/main.cy.ts.
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
*/
export function beforeCompareSnapshots(
/** 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("compareSnapshots", (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);
});
});
}
You may then use this function like:
const addCompareSnapshotCommand = require("cypress-visual-regression/dist/command");
const beforeCompareSnapshots = require("./commands/beforeCompareSnapshots");
addCompareSnapshotCommand({
errorThreshold: 0.1
});
// add a before hook to compareSnapshot (this must be called AFTER compareSnapshotCommand() so the command can be overriden)
beforeCompareSnapshots(
".chromatic-ignore,[data-chromatic='ignore']",
"._app-content"
);
In this example, we ignore the elements that are also ignored by 3rd party tool Chromatic.
Debug
set visualRegressionLogger
to true
to enable logging.