Test runner

Storybook test runner turns all of your stories into executable tests. It is powered by Jest and Playwright.

These tests run in a live browser and can be executed via the command line or your CI server.

Setup

The test-runner is a standalone, framework-agnostic utility that runs parallel to your Storybook. You will need to take some additional steps to set it up properly. Detailed below is our recommendation to configure and execute it.

Run the following command to install it.

Update your package.json scripts and enable the test runner.

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Start your Storybook with:

Storybook's test runner requires either a locally running Storybook instance or a published Storybook to run all the existing tests.

Finally, open a new terminal window and run the test-runner with:

Configure

Test runner offers zero-config support for Storybook. However, you can run test-storybook --eject for more fine-grained control. It generates a test-runner-jest.config.js file at the root of your project, which you can modify. Additionally, you can extend the generated configuration file and provide testEnvironmentOptions as the test runner also uses jest-playwright under the hood.

CLI Options

The test-runner is powered by Jest and accepts a subset of its CLI options (for example, --watch, --maxWorkers). If you're already using any of those flags in your project, you should be able to migrate them into Storybook's test-runner without any issues. Listed below are all the available flags and examples of using them.

OptionsDescription
--helpOutput usage information
test-storybook --help
-s, --index-jsonRun in index json mode. Automatically detected (requires a compatible Storybook)
test-storybook --index-json
--no-index-jsonDisables index json mode
test-storybook --no-index-json
-c, --config-dir [dir-name]Directory where to load Storybook configurations from
test-storybook -c .storybook
--watchRun in watch mode
test-storybook --watch
--watchAllWatch files for changes and rerun all tests when something changes.
test-storybook --watchAll
--coverageRuns coverage tests on your stories and components
test-storybook --coverage
--coverageDirectoryDirectory where to write coverage report output
test-storybook --coverage --coverageDirectory coverage/ui/storybook
--urlDefine the URL to run tests in. Useful for custom Storybook URLs
test-storybook --url http://the-storybook-url-here.com
--browsersDefine browsers to run tests in. One or multiple of: chromium, firefox, webkit
test-storybook --browsers firefox chromium
--maxWorkers [amount]Specifies the maximum number of workers the worker-pool will spawn for running tests
test-storybook --maxWorkers=2
--testTimeout [amount]Defines the maximum time in milliseconds that a test can run before it is automatically marked as failed. Useful for long-running tests
test-storybook --testTimeout=60000
--no-cacheDisable the cache
test-storybook --no-cache
--clearCacheDeletes the Jest cache directory and then exits without running tests
test-storybook --clearCache
--verboseDisplay individual test results with the test suite hierarchy
test-storybook --verbose
-u, --updateSnapshotUse this flag to re-record every snapshot that fails during this test run
test-storybook -u
--ejectCreates a local configuration file to override defaults of the test-runner
test-storybook --eject
--jsonPrints the test results in JSON. This mode will send all other test output and user messages to stderr.
test-storybook --json
--outputFileWrite test results to a file when the --json option is also specified.
test-storybook --json --outputFile results.json
--junitIndicates that test information should be reported in a junit file.
test-storybook --**junit**
--ciInstead of the regular behavior of storing a new snapshot automatically, it will fail the test and require Jest to be run with --updateSnapshot.
test-storybook --ci
--shard [index/count]Requires CI. Splits the test suite execution into multiple machines
test-storybook --shard=1/8
--failOnConsoleMakes tests fail on browser console errors
test-storybook --failOnConsole
--includeTagsExperimental feature
Defines a subset of stories to be tested if they match the enabled tags.
test-storybook --includeTags="test-only, pages"
--excludeTagsExperimental feature
Prevents stories from being tested if they match the provided tags.
test-storybook --excludeTags="no-tests, tokens"
--skipTagsExperimental feature
Configures the test runner to skip running tests for stories that match the provided tags.
test-storybook --skipTags="skip-test, layout"

Run tests against a deployed Storybook

By default, the test-runner assumes that you're running it against a locally served Storybook on port 6006. If you want to define a target URL to run against deployed Storybooks, you can use the --url flag or set the TARGET_URL environment variable. For example:

Set up CI to run tests

You can also configure the test-runner to run tests on a CI environment. Documented below are some recipes to help you get started.

Run against deployed Storybooks via Github Actions deployment

If you're publishing your Storybook with services such as Vercel or Netlify, they emit a deployment_status event in GitHub Actions. You can use it and set the deployment_status.target_url as the TARGET_URL environment variable. Here's how:

The published Storybook must be publicly available for this example to work. We recommend running the test server using the recipe below if it requires authentication.

Run against non-deployed Storybooks

You can use your CI provider (for example, GitHub Actions, GitLab Pipelines, CircleCI) to build and run the test runner against your built Storybook. Here's a recipe that relies on third-party libraries, that is to say, concurrently, http-server, and wait-on to build Storybook and run tests with the test-runner.

By default, Storybook outputs the build to the storybook-static directory. If you're using a different build directory, you'll need to adjust the recipe accordingly.

What's the difference between Chromatic and Test runner?

The test-runner is a generic testing tool that can run locally or on CI and be configured or extended to run all kinds of tests.

Chromatic is a cloud-based service that runs visual and interaction tests (and soon accessibility tests) without setting up the test runner. It also syncs with your git provider and manages access control for private projects.

However, you might want to pair the test runner and Chromatic in some cases.

  • Use it locally and Chromatic on your CI.
  • Use Chromatic for visual and interaction tests and run other custom tests using the test runner.

Advanced configuration

Test hook API

The test-runner renders a story and executes its play function if one exists. However, certain behaviors are impossible to achieve via the play function, which executes in the browser. For example, if you want the test-runner to take visual snapshots for you, this is possible via Playwright/Jest but must be executed in Node.

The test-runner exports test hooks that can be overridden globally to enable use cases like visual or DOM snapshots. These hooks give you access to the test lifecycle before and after the story is rendered. Listed below are the available hooks and an overview of how to use them.

HookDescription
preparePrepares the browser for tests
async prepare({ page, browserContext, testRunnerConfig }) {}
setupExecutes once before all the tests run
setup() {}
preVisitExecutes before a story is initially visited and rendered in the browser
async preVisit(page, context) {}
postVisitExecutes after the story is visited and fully rendered
async postVisit(page, context) {}

These test hooks are experimental and may be subject to breaking changes. We encourage you to test as much as possible within the story's play function.

To enable the hooks API, you'll need to add a new configuration file inside your Storybook directory and set them up as follows:

Except for the setup function, all other functions run asynchronously. Both preVisit and postVisit functions include two additional arguments, a Playwright page and a context object which contains the id, title, and the name of the story.

When the test-runner executes, your existing tests will go through the following lifecycle:

  • The setup function is executed before all the tests run.
  • The context object is generated containing the required information.
  • Playwright navigates to the story's page.
  • The preVisit function is executed.
  • The story is rendered, and any existing play functions are executed.
  • The postVisit function is executed.

(Experimental) Filter tests

When you run the test-runner on Storybook, it tests every story by default. However, if you want to filter the tests, you can use the tags configuration option. Storybook originally introduced this feature to generate automatic documentation for stories. But it can be further extended to configure the test-runner to run tests according to the provided tags using a similar configuration option or via CLI flags (e.g., --includeTags, --excludeTags, --skipTags), only available with the latest stable release (0.15 or higher). Listed below are the available options and an overview of how to use them.

OptionDescription
excludePrevents stories if they match the provided tags from being tested.
includeDefines a subset of stories only to be tested if they match the enabled tags.
skipSkips testing on stories if they match the provided tags.

Running tests with the CLI flags takes precedence over the options provided in the configuration file and will override the available options in the configuration file.

Disabling tests

If you want to prevent specific stories from being tested by the test-runner, you can configure your story with a custom tag, enable it to the test-runner configuration file or run the test-runner with the --excludeTags CLI flag and exclude them from testing. This is helpful when you want to exclude stories that are not yet ready for testing or are irrelevant to your tests. For example:

Run tests for a subset of stories

To allow the test-runner only to run tests on a specific story or subset of stories, you can configure the story with a custom tag, enable it in the test-runner configuration file or run the test-runner with the --includeTags CLI flag and include them in your tests. For example, if you wanted to run tests based on the test-only tag, you can adjust your configuration as follows:

Applying tags for the component's stories should either be done at the component level (using meta) or at the story level. Importing tags across stories is not supported in Storybook and won't work as intended.

Skip tests

If you want to skip running tests on a particular story or subset of stories, you can configure your story with a custom tag, enable it in the test-runner configuration file, or run the test-runner with the --skipTags CLI flag. Running tests with this option will cause the test-runner to ignore and flag them accordingly in the test results, indicating that the tests are temporarily disabled. For example:

Authentication for deployed Storybooks

If you use a secure hosting provider that requires authentication to host your Storybook, you may need to set HTTP headers. This is mainly because of how the test runner checks the status of the instance and the index of its stories through fetch requests and Playwright. To do this, you can modify the test-runner configuration file to include the getHttpHeaders function. This function takes the URL of the fetch calls and page visits as input and returns an object containing the headers that need to be set.

Helpers

The test-runner exports a few helpers that can be used to make your tests more readable and maintainable by accessing Storybook's internals (e.g., args, parameters). Listed below are the available helpers and an overview of how to use them.

Accessing story information with the test-runner

If you need to access information about the story, such as its parameters, the test-runner includes a helper function named getStoryContext that you can use to retrieve it. You can then use it to customize your tests further as needed. For example, if you need to configure Playwright's page viewport size to use the viewport size defined in the story's parameters, you can do so as follows:

Working with assets

If you're running a specific set of tests (e.g., image snapshot testing), the test-runner provides a helper function named waitForPageReady that you can use to ensure the page is fully loaded and ready before running the test. For example:

Index.json mode

The test-runner transforms your story files into tests when testing a local Storybook. For a remote Storybook, it uses the Storybook's index.json (formerly stories.json) file (a static index of all the stories) to run the tests.

Why?

Suppose you run into a situation where the local and remote Storybooks appear out of sync, or you might not even have access to the code. In that case, the index.json file is guaranteed to be the most accurate representation of the deployed Storybook you are testing. To test a local Storybook using this feature, use the --index-json flag as follows:

The index.json mode is not compatible with the watch mode.

If you need to disable it, use the --no-index-json flag:

How do I check if my Storybook has a index.json file?

Index.json mode requires a index.json file. Open a browser window and navigate to your deployed Storybook instance (for example, https://your-storybook-url-here.com/index.json). You should see a JSON file that starts with a "v": 3 key, immediately followed by another key called "stories", which contains a map of story IDs to JSON objects. If that is the case, your Storybook supports index.json mode.


Troubleshooting

The test runner seems flaky and keeps timing out

If your tests time out with the following message:

Terminal
Loading...

It might be that Playwright couldn't handle testing the number of stories you have in your project. Perhaps you have a large number of stories, or your CI environment has a really low RAM configuration. In such cases, you should limit the number of workers that run in parallel by adjusting your command as follows:

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The error output in the CLI is too short

By default, the test runner truncates error outputs at 1000 characters, and you can check the full output directly in Storybook in the browser. However, if you want to change that limit, you can do so by setting the DEBUG_PRINT_LIMIT environment variable to a number of your choosing, for example, DEBUG_PRINT_LIMIT=5000 yarn test-storybook.

Run the test runner in other CI environments

As the test runner is based on Playwright, you might need to use specific docker images or other configurations depending on your CI setup. In that case, you can refer to the Playwright CI docs for more information.

Tests filtered by tags are incorrectly executed

If you've enabled filtering tests with tags and provided similar tags to the include and exclude lists, the test-runner will execute the tests based on the exclude list and ignore the include list. To avoid this, make sure the tags provided to the include and exclude lists differ.

The test runner doesn't support Yarn PnP out of the box

If you've enabled the test-runner in a project running on a newer version of Yarn with Plug'n'Play (PnP) enabled, the test-runner might not work as expected and may generate the following error when running tests:

Terminal
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This is due to the test-runner using the community-maintained package jest-playwright-preset that still needs to support this feature. To solve this, you can either switch the nodeLinker setting to node-modules or install Playwright as a direct dependency in your project, followed by adding the browser binaries via the install command.

Learn about other UI tests

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