Storybook test runner
Test runner for Storybook stories
npm install @storybook/test-runner
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Storybook Test Runner

Storybook test runner turns all of your stories into executable tests.

Table of Contents

Features

  • ⚡️ Zero config setup
  • 💨 Smoke test all stories
  • ▶️ Test stories with play functions
  • 🏃 Test your stories in parallel in a headless browser
  • 👷 Get feedback from error with a link directly to the story
  • 🐛 Debug them visually and interactively in a live browser with addon-interactions
  • 🎭 Powered by Jest and Playwright
  • 👀 Watch mode, filters, and the conveniences you'd expect
  • 📔 Code coverage reports

How it works

See the announcement of Interaction Testing with Storybook in detail in this blog post or watch this video to see it in action.

The Storybook test runner uses Jest as a runner, and Playwright as a testing framework. Each one of your .stories files is transformed into a spec file, and each story becomes a test, which is run in a headless browser.

The test runner is simple in design – it just visits each story from a running Storybook instance and makes sure the component is not failing:

  • For stories without a play function, it verifies whether the story rendered without any errors. This is essentially a smoke test.
  • For those with a play function, it also checks for errors in the play function and that all assertions passed. This is essentially an interaction test.

If there are any failures, the test runner will provide an output with the error, alongside with a link to the failing story, so you can see the error yourself and debug it directly in the browser:

Getting started

  1. Install the test runner and the interactions addon in Storybook:
yarn add @storybook/test-runner -D

Jest is a peer dependency. If you don't have it, also install it

yarn add jest -D
1.1 Optional instructions to install the Interactions addon for visual debugging of play functions
yarn add @storybook/addon-interactions @storybook/jest @storybook/testing-library -D

Then add it to your .storybook/main.js config and enable debugging:

module.exports = {
  addons: ['@storybook/addon-interactions'],
  features: {
    interactionsDebugger: true,
  },
};
  1. Add a test-storybook script to your package.json
{
  "scripts": {
    "test-storybook": "test-storybook"
  }
}
  1. Run Storybook (the test runner runs against a running Storybook instance):
yarn storybook
  1. Run the test runner:
yarn test-storybook

NOTE: The runner assumes that your Storybook is running on port 6006. If you're running Storybook in another port, either use --url or set the TARGET_URL before running your command like:

yarn test-storybook --url http://localhost:9009
or
TARGET_URL=http://localhost:9009 yarn test-storybook

CLI Options

Usage: test-storybook [options]
Options Description
--help Output usage information
test-storybook --help
-i, --index-json Run in index json mode. Automatically detected (requires a compatible Storybook)
test-storybook --index-json
--no-index-json Disables index json mode
test-storybook --no-index-json
-c, --config-dir [dir-name] Directory where to load Storybook configurations from
test-storybook -c .storybook
--watch Watch files for changes and rerun tests related to changed files.
test-storybook --watch
--watchAll Watch files for changes and rerun all tests when something changes.
test-storybook --watchAll
--coverage Indicates that test coverage information should be collected and reported in the output
test-storybook --coverage
--url Define the URL to run tests in. Useful for custom Storybook URLs
test-storybook --url http://the-storybook-url-here.com
--browsers Define 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
--no-cache Disable the cache
test-storybook --no-cache
--clearCache Deletes the Jest cache directory and then exits without running tests
test-storybook --clearCache
--verbose Display individual test results with the test suite hierarchy
test-storybook --verbose
-u, --updateSnapshot Use this flag to re-record every snapshot that fails during this test run
test-storybook -u
--eject Creates a local configuration file to override defaults of the test-runner
test-storybook --eject

Configuration

The test runner is based on Jest and will accept the CLI options that Jest does, like --watch, --watchAll, --maxWorkers, etc.

The test runner works out of the box, but if you want better control over its configuration, you can run test-storybook --eject to create a local test-runner-jest.config.js file in the root folder of your project, which will be used by the test runner.

The test runner uses jest-playwright and you can pass testEnvironmentOptions to further configure it, such as how it's done above to run tests against all browsers instead of just chromium. For this you must eject the test runner configuration.

Running 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 so it runs against deployed Storybooks, you can do so by passing the TARGET_URL environment variable:

TARGET_URL=https://the-storybook-url-here.com yarn test-storybook

Or by using the --url flag:

yarn test-storybook --url https://the-storybook-url-here.com

Index.json mode

By default, the test runner transforms your story files into tests. It also supports a secondary "index.json mode" which runs directly against your Storybook's index data, which dependending on your Storybook version is located in a stories.json or index.json, a static index of all the stories.

This is particularly useful for running against a deployed storybook because index.json is guaranteed to be in sync with the Storybook you are testing. In the default, story file-based mode, your local story files may be out of sync – or you might not even have access to the source code. Furthermore, it is not possible to run the test-runner directly against .mdx stories, and index.json mode must be used.

If you're using Storybook 7.0

To run in index.json mode, first make sure your Storybook has a v4 index.json file. You can find it when navigating to:

https://your-storybook-url-here.com/index.json

It should be a JSON file and the first key should be "v": 4 followed by a key called "entries" containing a map of story IDs to JSON objects.

In Storybok 7.0, index.json is enabled by default, unless you are using the storiesOf() syntax, in which case it is not supported.

On Storybook 6.4 and 6.5, to run in index.json mode, first make sure your Storybook has a file called stories.json that has "v": 3, available at:

https://your-storybook-url-here.com/stories.json

If your Storybook does not have a stories.json file, you can generate one, provided:

  • You are running Storybook 6.4 or above
  • You are not using storiesOf stories

To enable stories.json in your Storybook, set the buildStoriesJson feature flag in .storybook/main.js:

module.exports = {
  features: { buildStoriesJson: true },
};

Once you have a valid stories.json file, your Storybook will be compatible with the "index.json mode".

By default, the test runner will detect whether your Storybook URL is local or remote, and if it is remote, it will run in "index.json mode" automatically. To disable it, you can pass the --no-index-json flag:

yarn test-storybook --no-index-json

If you are running tests against a local Storybook but for some reason want to run in "index.json mode", you can pass the --index-json flag:

yarn test-storybook --index-json

NOTE: index.json mode is not compatible with watch mode.

Running in CI

If you want to add the test-runner to CI, there are a couple of ways to do so:

1. Running against deployed Storybooks on Github Actions deployment

On Github actions, once services like Vercel, Netlify and others do deployment runs, they follow a pattern of emitting a deployment_status event containing the newly generated URL under deployment_status.target_url. You can use that URL and set it as TARGET_URL for the test-runner.

Here's an example of an action to run tests based on that:

name: Storybook Tests
on: deployment_status
jobs:
  test:
    timeout-minutes: 60
    runs-on: ubuntu-latest
    if: github.event.deployment_status.state == 'success'
    steps:
      - uses: actions/checkout@v2
      - uses: actions/setup-node@v2
        with:
          node-version: '14.x'
      - name: Install dependencies
        run: yarn
      - name: Run Storybook tests
        run: yarn test-storybook
        env:
          TARGET_URL: '${{ github.event.deployment_status.target_url }}'

NOTE: If you're running the test-runner against a TARGET_URL of a remotely deployed Storybook (e.g. Chromatic), make sure that the URL loads a publicly available Storybook. Does it load correctly when opened in incognito mode on your browser? If your deployed Storybook is private and has authentication layers, the test-runner will hit them and thus not be able to access your stories. If that is the case, use the next option instead.

2. Running against locally built Storybooks in CI

In order to build and run tests against your Storybook in CI, you might need to use a combination of commands involving the concurrently, http-server and wait-on libraries. Here's a recipe that does the following: Storybook is built and served locally, and once it is ready, the test runner will run against it.

{
  "test-storybook:ci": "concurrently -k -s first -n \"SB,TEST\" -c \"magenta,blue\" \"yarn build-storybook --quiet && npx http-server storybook-static --port 6006 --silent\" \"wait-on tcp:6006 && yarn test-storybook\""
}

And then you can essentially run test-storybook:ci in your CI:

name: Storybook Tests
on: push
jobs:
  test:
    timeout-minutes: 60
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2
      - uses: actions/setup-node@v2
        with:
          node-version: '14.x'
      - name: Install dependencies
        run: yarn
      - name: Run Storybook tests
        run: yarn test-storybook:ci

NOTE: Building Storybook locally makes it simple to test Storybooks that could be available remotely, but are under authentication layers. If you also deploy your Storybooks somewhere (e.g. Chromatic, Vercel, etc.), the Storybook URL can still be useful with the test-runner. You can pass it to the REFERENCE_URL environment variable when running the test-storybook command, and if a story fails, the test-runner will provide a helpful message with the link to the story in your published Storybook instead.

Setting up code coverage

The test runner supports code coverage with the --coverage flag or STORYBOOK_COLLECT_COVERAGE environment variable. The pre-requisite is that your components are instrumented using istanbul.

1 - Instrument the code

Given that your components' code runs in the context of a real browser, they have to be instrumented so that the test runner is able to collect coverage. This is done by configuring istanbul in your Storybook. You can achieve that in two different ways:

Using @storybook/addon-coverage

For select frameworks with Webpack (React, Preact, HTML, Web components and Vue) you can use the @storybook/addon-coverage addon, which will automatically configure the plugin for you.

Install @storybook/addon-coverage:

yarn add -D @storybook/addon-coverage

And register it in your .storybook/main.js file:

// .storybook/main.js
module.exports = {
  // ...rest of your code here
  addons: [
    "@storybook/addon-coverage",
  ]
};

The addon has default options that might suffice to your project, however if you want to customize the addon you can see how it's done here.

Manually configuring istanbul

Some frameworks or Storybook builders (e.g. Vite) might not automatically accept babel plugins. In that case, you will have to manually configure whatever flavor of istanbul (Rollup, Vite, Webpack loader) your project might require. You can find recipes in this repository that include many different configurations and steps on how to set up coverage in each of them.

2 - Run tests with --coverage flag

After setting up instrumentation, run Storybook then run the test-runner with --coverage:

yarn test-storybook --coverage

The test runner will report the results in the CLI and generate a coverage/storybook/coverage-storybook.json file which can be used by nyc.

If you want to generate reports with different reporters, you can use nyc and point it to the folder which contains the Storybook coverage file. nyc is a dependency of the test runner so you will already have it in your project.

Here's an example generating an lcov report:

npx nyc report --reporter=lcov -t coverage/storybook --report-dir coverage/storybook

This will generate a more detailed, interactive coverage summary that you can access at coverage/storybook/index.html file which can be explored and will show the coverage in detail:

The nyc command will respect nyc configuration files if you have them in your project.

If you want certain parts of your code to be deliberately ignored, you can use istanbul parsing hints.

3 - Merging code coverage with coverage from other tools

The test runner reports coverage related to the coverage/storybook/coverage-storybook.json file. This is by design, showing you the coverage which is tested while running Storybook.

Now, you might have other tests (e.g. unit tests) which are not covered in Storybook but are covered when running tests with Jest, which you might also generate coverage files from, for instance. In such cases, if you are using tools like Codecov to automate reporting, the coverage files will be detected automatically and if there are multiple files in the coverage folder, they will be merged automatically.

Alternatively, in case you want to merge coverages from other tools, you should:

1 - move or copy the coverage/storybook/coverage-storybook.json into coverage/coverage-storybook.json; 2 - run nyc report against the coverage folder.

Here's an example on how to achieve that:

{
  "scripts": {
    "test:coverage": "jest --coverage",
    "test-storybook:coverage": "test-storybook --coverage",
    "coverage-report": "cp coverage/storybook/coverage-storybook.json coverage/coverage-storybook.json && nyc report --reporter=html -t coverage --report-dir coverage"
  }
}

Experimental test hook API

The test runner renders a story and executes its play function if one exists. However, there are certain behaviors that are not possible 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 something that is possible via Playwright/Jest, but must be executed in Node.

To enable use cases like visual or DOM snapshots, the test runner exports test hooks that can be overridden globally. These hooks give you access to the test lifecycle before and after the story is rendered.

There are three hooks: setup, preRender, and postRender. setup executes once before all the tests run. preRender and postRender execute within a test before and after a story is rendered.

The render functions are async functions that receive a Playwright Page and a context object with the current story id, title, and name. They are globally settable by @storybook/test-runner's setPreRender and setPostRender APIs.

All three functions can be set up in the configuration file .storybook/test-runner.js which can optionally export any of these functions.

NOTE: 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.

DOM snapshot recipe

The postRender function provides a Playwright page instance, of which you can use for DOM snapshot testing:

// .storybook/test-runner.js
module.exports = {
  async postRender(page, context) {
    // the #root element wraps the story
    const elementHandler = await page.$('#root');
    const innerHTML = await elementHandler.innerHTML();
    expect(innerHTML).toMatchSnapshot();
  },
};

When running with --stories-json, tests get generated in a temporary folder and snapshots get stored alongside. You will need to --eject and configure a custom snapshotResolver to store them elsewhere, e.g. in your working directory:

const path = require('path');

module.exports = {
  resolveSnapshotPath: (testPath, snapshotExtension) =>
    path.join(process.cwd(), '__snapshots__', path.basename(testPath) + snapshotExtension),
  resolveTestPath: (snapshotFilePath, snapshotExtension) =>
    path.join(process.env.TEST_ROOT, path.basename(snapshotFilePath, snapshotExtension)),
  testPathForConsistencyCheck: path.join(process.env.TEST_ROOT, 'example.test.js'),
};

Image snapshot recipe

Here's a slightly different recipe for image snapshot testing:

// .storybook/test-runner.js
const { toMatchImageSnapshot } = require('jest-image-snapshot');

const customSnapshotsDir = `${process.cwd()}/__snapshots__`;

module.exports = {
  setup() {
    expect.extend({ toMatchImageSnapshot });
  },
  async postRender(page, context) {
    const image = await page.screenshot();
    expect(image).toMatchImageSnapshot({
      customSnapshotsDir,
      customSnapshotIdentifier: context.id,
    });
  },
};

There is also an exported TestRunnerConfig type available for TypeScript users.

Render lifecycle

To visualize the test lifecycle, consider a simplified version of the test code automatically generated for each story in your Storybook:

it('button--basic', async () => {
  // filled in with data for the current story
  const context = { id: 'button--basic', title: 'Button', name: 'Basic' };

  // playwright page https://playwright.dev/docs/pages
  await page.goto(STORYBOOK_URL);

  // pre-render hook
  if (preRender) await preRender(page, context);

  // render the story and run its play function (if applicable)
  await page.execute('render', context);

  // post-render hook
  if (postRender) await postRender(page, context);
});

Global utility functions

While running tests using the hooks, you might want to get information from a story, such as the parameters passed to it, or its args. The test runner now provides a getStoryContext utility function that fetches the story context for the current story:

await getStoryContext(page, context);

You can use it for multiple use cases, and here's an example that combines the story context and accessibility testing:

// .storybook/test-runner.js
const { getStoryContext } = require('@storybook/test-runner');
const { injectAxe, checkA11y } = require('axe-playwright');
 
module.exports = {
 async preRender(page, context) {
   await injectAxe(page);
 },
 async postRender(page, context) {
  // Get entire context of a story, including parameters, args, argTypes, etc.
  const storyContext = await getStoryContext(page, context);

  // Do not test a11y for stories that disable a11y
  if (storyContext.parameters?.a11y?.disable) {
    return;
  }
  
   await checkA11y(page, '#root', {
     detailedReport: true,
     detailedReportOptions: {
       html: true,
     },
     // pass axe options defined in @storybook/addon-a11y
     axeOptions: storyContext.parameters?.a11y?.options
   })
 },
};

Troubleshooting

Jest 27 support

jest-playwright 2.0.0 has a breaking change of requiring Jest 28+. To support older versions of Jest you will need to use Yarn resolutions or NPM overrides to downgrade jest-playwright-preset to ^1.7.2.

// Yarn resolutions in your projects package.json
{
  "resolutions": {
    "jest-playwright-preset": "^1.7.2"
  }
}
// NPM overrides in your projects package.json
{
  "overrides": {
    "@storybook/test-runner": {
      "jest-playwright-preset": "^1.7.2"
    }
  }
}

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. If you do want to change that limit, however, 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.

The test runner seems flaky and keeps timing out

If your tests are timing out with Timeout - Async callback was not invoked within the 15000 ms timeout specified by jest.setTimeout, it might be that playwright couldn't handle to test the amount of stories you have in your project. Maybe you have a large amount of stories or your CI has a really low RAM configuration.

In either way, to fix it you should limit the amount of workers that run in parallel by passing the --maxWorkers option to your command:

{
  "test-storybook:ci": "concurrently -k -s first -n \"SB,TEST\" -c \"magenta,blue\" \"yarn build-storybook --quiet && npx http-server storybook-static --port 6006 --silent\" \"wait-on tcp:6006 && yarn test-storybook --maxWorkers=2\""
}

The test runner reports "No tests found" running on a Windows CI

There is currently a bug in Jest which means tests cannot be on a separate drive than the project. To work around this you will need to set the TEMP environment variable to a temporary folder on the same drive as your project. Here's what that would look like on GitHub Actions:

env:
  # Workaround for https://github.com/facebook/jest/issues/8536
  TEMP: ${{ runner.temp }}

Adding the test runner to other CI environments

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

Future work

Future plans involve adding support for the following features:

  • 📄 Run addon reports