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Automate Chromatic with CircleCI

Chromatic’s automation can be included as part of your CircleCI job with relative ease.

Setup

To integrate Chromatic with your existing workflow, you’ll need to add the following:

.circleci/config.yml
version: 2.1

executors:
  chromatic-ui-testing:
    docker:
      - image: cimg/node:20.12.2
    working_directory: ~/repo

jobs:
  Chromatic:
    executor: chromatic-ui-testing
    steps:
      - checkout
      - restore_cache:
          keys:
            - v1-dependencies-{{ checksum "package.json" }}
            - v1-dependencies-
      # ⚠️ See your package manager's documentation for the correct command to install dependencies in a CI environment.
      - run: npm ci
      - run: npx chromatic
      - save_cache:
          name: Save NPM cache
          paths:
            - ~/.npm
          key: v1-dependencies-{{ checksum "package.json" }}

workflows:
  UI_Tests:
    jobs:
      - Chromatic

We recommend saving the project token as an environment variable named CHROMATIC_PROJECT_TOKEN for security reasons. When the Chromatic CLI is executed, it will read the environment variable automatically without any additional flags. Refer to the official CircleCI environment variables documentation to learn more about it.

Run Chromatic on specific branches

If you need to customize your workflow to run Chromatic on specific branches, adjust your workflow like so:

.circleci/config.yml
# Other required configuration

jobs:
# Other jobs implemented in the workflow

workflows:
  # 👇 Adds Chromatic to the workflow
  UI_Tests:
    jobs:
      - Chromatic:
          filters: # 👈 Filters the execution to run only on the main branch
            branches:
              only: main

Read the official CircleCI conditional job execution documentation.

Now Chromatic will only run in the main branch.

Run Chromatic on large projects

Chromatic is prepared to handle large file uploads (with a limit of 5000 files, including stories and assets). If your project exceeds this limit, we recommend adjusting your workflow and run the chromatic command with the --zip flag to compress your build before uploading it. For example:

.circleci/config.yml
# Other required configuration

jobs:
  # Other jobs

  # 👇 Adds Chromatic as a job
  Chromatic:
    # Other configuration
    steps:
      # Other job steps

      # 👇 Runs Chromatic with the flag to compress the build output.
      - run: npx chromatic --zip
# Workflows here

Run Chromatic on monorepos

Chromatic can be run on monorepos that have multiple subprojects. Each subproject will need it’s own project token stored as an environment variable.

Prerequisites

  1. Ensure that you’re in the correct working directory for the subproject.
  2. Have build-storybook npm script in the subproject’s package.json file OR explicitly name the script using the buildScriptName parameter and make sure the script is listed in the subproject’s package.json file.

If you’ve already built your Storybook in a separate CI step, you can alternatively point the action at the build output using the storybookBuildDir parameter.

.circleci/config.yml
# Other required configuration

jobs:
  # Other jobs

  # 👇 Adds Chromatic as a job
  Chromatic:
    # Other configuration
    steps:
      # Other job steps

      # 👇 Runs Chromatic sequentially for each monorepo subproject.
      - run:
          command: cd packages/project_1 && npx chromatic
          environment:
            CHROMATIC_PROJECT_TOKEN: $CHROMATIC_PROJECT_TOKEN_1
      - run:
          command: cd packages/project_2 && npx chromatic
          environment:
            CHROMATIC_PROJECT_TOKEN: $CHROMATIC_PROJECT_TOKEN_2
# Workflows here

Additional paralellization can be achieved when configuring your workflow to run Chromatic on multiple subprojects. Read the official CircleCI documentation.

Enable TurboSnap

TurboSnap is an advanced Chromatic feature implemented to improve the build time for large projects, disabled by default once you add Chromatic to your CI environment. To enable it, you’ll need to adjust your existing workflow and run the chromatic command with the --only-changed flag as follows:

.circleci/config.yml
# Other required configuration

jobs:
  # Other jobs

  # 👇 Adds Chromatic as a job
  Chromatic:
    # Other configuration
    steps:
      # Other job steps

      # 👇 Enables Chromatic's TurboSnap feature.
      - run: npx chromatic --only-changed
# Workflows here

TurboSnap is highly customizable and can be configured to fit your requirements. For more information, read our documentation.

External Pull Requests

See this CircleCI documentation for workflows related to pull requests from forked repositories.

Advanced configuration

For a more complex workflow configuration, checkout this Chromatic CircleCI Orb made by a customer.

In there you’ll find various scenarios that you can use depending on your needs.

UI Test and UI Review

UI Tests and UI Review rely on branch and baseline detection to keep track of snapshots. We recommend the following configuration.

Command exit code for “required” checks

If you are using pull request statuses as required checks before merging, you may not want your Circle CI job to fail if test snapshots render without errors (but with changes). To achieve this, pass the flag --exit-zero-on-changes to the chromatic command, and your job will continue in such cases. For example:

.circleci/config.yml
# Other required configuration

jobs:
  # Other jobs

  # 👇 Adds Chromatic as a job
  Chromatic:
    # Other configuration
    steps:
      # Other job steps

      # 👇 Runs Chromatic with the flag to prevent workflow failure
      - run: npx chromatic --exit-zero-on-changes
# Workflows here

Read our configuration reference documentation.

When using --exit-zero-on-changes your job will still stop and fail if your Storybook contains stories that error. If you’d prefer Chromatic never to block your job, you can use npx chromatic || true.

Re-run failed builds after verifying UI test results

Builds that contain visual changes need to be verified. They will fail if you are not using --exit-zero-on-changes. Once you accept all the changes, re-run the workflow and the chromatic-deployment job will pass.

If you deny any change, you will need to make the necessary code changes to fix the test (and thus start a new build) to get Chromatic to pass again.

Maintain a clean “main” branch

A clean main branch is a development best practice and highly recommended for Chromatic. This means testing your main branch to ensure builds are passing. It’s important to note that baselines will not persist through branching and merging unless you test your main branch.

If the builds are a result of direct commits to main, you will need to accept changes to keep the main branch clean. If they’re merged from feature-branches, you will need to make sure those branches are passing before you merge into main.

Squash/rebase merge and the “main” branch

We use GitHub, GitLab, and Bitbucket APIs respectively to detect squashing and rebasing so your baselines match your expectations no matter your Git workflow (see Branching and Baselines for more details).

If you’re using this functionality but notice the incoming changes were not accepted as baselines in Chromatic, then you’ll need to adjust the chromatic command and include the --auto-accept-changes flag. For example:

.circleci/config.yml
# Other required configuration

# 👇 Checks if the current branch is not the main and runs Chromatic
if [ "${CIRCLE_BRANCH}" != "main" ];
then
  npx chromatic
else
  # 👇 Checks if the current branch is main and runs Chromatic with the flag to accept all changes
  npx chromatic --auto-accept-changes
fi

Read our configuration reference documentation.

Including the --auto-accept-changes flag ensures all incoming changes will be accepted as baselines. Additionally, you’ll maintain a clean main branch.

If you want to test the changes introduced by the rebased branch, you can adjust your workflow and include a new step with the ignore-last-build-on-branch flag. For example:

.circleci/config.yml
# Other required configuration

jobs:
  # Other jobs

  # 👇 Adds Chromatic as a job
  Chromatic:
    # Other configuration
    steps:
      # Other job steps

      # 👇 Option to skip the last build on target branch
      - run: npx chromatic --ignore-last-build-on-branch=my-branch
# Workflows here

Including the --ignore-last-build-on-branch flag ensures the latest build for the specific branch is not used as a baseline.

Run Chromatic on external forks of open source projects

You can enable PR checks for external forks by sharing your project token where you configured the Chromatic command (often in package.json or in the pipeline step).

Sharing project tokens allows contributors and others to run Chromatic builds on your project, consuming your snapshot quota. They cannot access your account, settings, or accept baselines. This can be an acceptable tradeoff for open source projects that value community contributions.

Skipping builds for certain branches

Sometimes you might want to skip running a build for a certain branch, but still have Chromatic mark the latest commit on that branch as “passed”. Otherwise pull requests could be blocked due to required checks that remain pending. To avoid this issue, you can run chromatic with the --skip flag. This flag accepts a branch name or glob pattern.

One use case for this feature is skipping builds for branches created by a bot. For instance, Dependabot automatically updates a projects dependencies. Although some dependencies can result in UI changes, you might not find it worthwhile to run Chromatic for every single dependency update. Instead, you could rely on Chromatic running against the main or develop branch.

To skip builds for dependabot branches, use the following:

npx chromatic --skip 'dependabot/**'

Read our configuration reference documentation.

To apply this to multiple branches, use an “extended glob”. See the globs guide for details.

npx chromatic --skip '@(renovate/**|dependabot/**)'
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