chromatic

What is chromatic?

The npm package 'chromatic' is a tool designed to help developers automate visual testing for their UI components. It captures snapshots of components and runs visual regression tests to ensure that changes do not break the visual appearance of applications. Chromatic integrates with Storybook to manage component libraries and streamline the testing process.

What are chromatic's main functionalities?

Visual Testing

This code sample demonstrates how to add a visual test for a simple button component using Chromatic with Storybook. The 'withChromatic' decorator is used to enable Chromatic's snapshot capabilities for the component.

import { storiesOf } from '@storybook/react';
import { withChromatic } from 'chromatic/isolated';

storiesOf('Button', module)
  .addDecorator(withChromatic)
  .add('default', () => <button>Click me</button>);

Snapshot Management

This code configures Chromatic to take snapshots after a delay and at specified screen widths, facilitating responsive visual testing. It helps in managing how snapshots are captured based on different device widths.

import { configure } from '@storybook/react';
import { setChromaticOptions } from 'chromatic';

setChromaticOptions({
  delay: 300, // Delay in ms before taking a snapshot
  widths: [320, 1200] // Array of widths for responsive testing
});

configure(() => require('./stories'), module);

Other packages similar to chromatic

storybook

Storybook is a user interface development environment and playground for UI components. It facilitates building UI components in isolation and structuring a component library. While it does not offer visual regression testing by itself, it is often used in conjunction with Chromatic to provide that functionality.

percy

Percy by BrowserStack is a visual testing and review platform that integrates with your CI/CD pipeline. It captures screenshots of web pages and components, compares them against the baseline, and highlights visual changes. Percy offers a more comprehensive CI/CD integration compared to Chromatic, which is more tightly coupled with Storybook.

backstopjs

BackstopJS automates visual regression testing of web applications by comparing DOM screenshots over time. It is a standalone tool that can be used without Storybook, providing a different approach to visual testing compared to Chromatic's dependency on Storybook for component management.

README

Chromatic CLI

Publishes your Storybook to Chromatic and kicks off tests if they're enabled.

Documentation

👉 Read the Chromatic CLI docs

📝 View the Changelog

Contributing

Contributions of any kind are welcome! We're available to chat via the Intercom widget on the documentation site.

Compatibility & versioning

Compatibility is guaranteed between this package and Chromatic like so:

• Production Chromatic ensures it’s compatible with what’s on npm
• What's on the Git tag is equal to what's published on npm for that version
• This package ensures it’s compatible with production Chromatic

To facilitate upgrading in the future, removing and adding features, this is the process:

• Any new features will have to be on Chromatic production before they could be used in this package
• We can add feature flags to be able to test new functionality
• Chromatic production can not remove any features this package depends on until after the usage has been removed from this package in addition to a grace period to allow users to upgrade

Building and running locally

1. Ensure all dependencies are installed with yarn install
2. Build + watch the code locally: yarn dev
3. Run a build of all the CLI's stories against a Chromatic project: yarn chromatic -t <token>.

Running against staging

CHROMATIC_INDEX_URL=https://index.staging-chromatic.com yarn chromatic -t <token>

Running against development

To test against a local development version of the Chromatic stack, use

CHROMATIC_INDEX_URL=https://index.dev-chromatic.com yarn chromatic -t <token>

To only test a small number of test stories as a smoke test, use:

SMOKE_TEST=1 CHROMATIC_INDEX_URL=https://index.dev-chromatic.com yarn chromatic -t <token>

Publishing a new version

We use auto to automate the release process. Versions are bumped, tags are created and the changelog is updated automatically. A new release goes out whenever a PR is merged to main. A PR must have exactly one of the following labels before merging:

• major triggers a major version bump
• minor triggers a minor version bump
• patch triggers a patch version bump

Additionally, a PR may have exactly one of these labels:

• release creates a latest rather than a next release (see below)
• skip-release does not create a release at all

We have three types of releases:

• latest releases are the general audience production releases, used by most people. Automatically created when merging a PR with the release label.
• next releases should be valid, working releases that can potentially be used by early adopters of new features, for example to handle a support request. Automatically created when merging a PR without the release and skip-release labels.
• canary releases are intended for testing purposes and should not be used in production, as they may only work against a staging or dev environment. Automatically created on every PR, but does not auto-publush the GitHub Action.

For GitHub Actions, we publish chromaui/action-next and chromaui/action-canary. The latter is only published manually, rather than for every PR.

A script is provided to manually publish the GitHub Action, though it's typically only necessary for action-canary releases:

yarn publish-action <canary|next|latest>