Write snapshot tests

Snapshot tests compare the rendered markup of every story against known baselines. It’s a way to identify markup changes that trigger rendering errors and warnings.

Storybook is a helpful tool for snapshot testing because every story is essentially a test specification. Any time you write or update a story, you get a snapshot test for free.

Example Snapshot test

If you're upgrading to Storybook 8.0 and were using the Storyshots addon for snapshot testing, it was officially deprecated and removed with this release. See the migration guide for more information.

Automate snapshot tests with the test-runner

Storybook test-runner turns all of your stories into executable tests. Powered by Jest and Playwright. It's a standalone, framework-agnostic utility that runs parallel to your Storybook. It enables you to run multiple testing patterns in a multi-browser environment, including interaction testing with the play function, DOM snapshot, and accessibility testing.

Setup

To enable snapshot testing with the test-runner, you'll need to take additional steps to set it up properly. We recommend you go through the test-runner documentation before proceeding with the rest of the required configuration to learn more about the available options and APIs.

Add a new configuration file inside your Storybook directory with the following inside:

The postVisit hook allows you to extend the test runner's default configuration. Read more about them here.

When you execute the test-runner (for example, with yarn test-storybook), it will run through all of your stories and run the snapshot tests, generating a snapshot file for each story in your project located in the __snapshots__ directory.

Configure

Out of the box, the test-runner provides an inbuilt snapshot testing configuration covering most use cases. You can also fine-tune the configuration to fit your needs via test-storybook --eject or by creating a test-runner-jest.config.js file at the root of your project.

Override the default snapshot directory

The test-runner uses a specific naming convention and path for the generated snapshot files by default. If you need to customize the snapshot directory, you can define a custom snapshot resolver to specify the directory where the snapshots are stored.

Create a snapshot-resolver.js file to implement a custom snapshot resolver:

Update the test-runner-jest.config.js file and enable the snapshotResolver option to use the custom snapshot resolver:

When the test-runner is executed, it will cycle through all of your stories and run the snapshot tests, generating a snapshot file for each story in your project located in the custom directory you specified.

Customize snapshot serialization

By default, the test-runner uses jest-serializer-html to serialize HTML snapshots. This may cause issues if you use specific CSS-in-JS libraries like Emotion, Angular's ng attributes, or similar libraries that generate hash-based identifiers for CSS classes. If you need to customize the serialization of your snapshots, you can define a custom snapshot serializer to specify how the snapshots are serialized.

Create a snapshot-serializer.js file to implement a custom snapshot serializer:

Update the test-runner-jest.config.js file and enable the snapshotSerializers option to use the custom snapshot resolver:

When the test-runner executes your tests, it will introspect the resulting HTML, replacing the dynamically generated attributes with the static ones provided by the regular expression in the custom serializer file before snapshotting the component. This ensures that the snapshots are consistent across different test runs.

Snapshot tests with Portable Stories

Storybook provides a composeStories utility that helps convert stories from a test file into renderable elements that can be reused in your Node tests with JSDOM. It also allows you to apply other Storybook features that you have enabled your project (e.g., decorators, args) into your tests, enabling you to reuse your stories in your testing environment of choice (e.g., Jest, Vitest), ensuring your tests are always in sync with your stories without having to rewrite them. This is what we refer to as portable stories in Storybook.

Configure

By default, Storybook offers a zero-config setup for React, Vue, and other frameworks via addons, allowing you to run your stories as tests with your testing environment of choice. However, if you're running tests and you've set up specific configurations in your Storybook instance (e.g., global decorators, parameters) that you want to use in your tests, you'll need to extend your test setup to include these configurations. To do so, create a setup.js|ts file as follows:

Update your test configuration file (e.g., vite.config.js|ts) if you're using Vitest or your test script if you're using Jest:

Run tests on a single story

If you need to run tests on a single story, you can use the composeStories function from the appropriate framework to process it and apply any configuration you've defined in your stories (e.g., decorators, args) and combine it with your testing environment to generate a snapshot file. For example, if you're working on a component and you want to test its default state, ensuring the expected DOM structure doesn't change, here's how you could write your test:

Execute tests on multiple stories

You can also use the composeStories function to test multiple stories. This is useful when you want to extend your test coverage to generate snapshots for the different states of the components in your project. To do so, you can write your test as follows:

When your tests are executed in your testing environment, they will generate a single snapshot file with all the stories in your project (i.e.,storybook.test.ts|js.snap). However, if you need, you can extend your test file to generate individual snapshot files for each story in your project with Vitest's toMatchFileSnapshot API or Jest's jest-specific-snapshot package. For example:

What’s the difference between snapshot tests and visual tests?

Visual tests capture images of stories and compare them against image baselines. Snapshot tests take DOM snapshots and compare them against DOM baselines. Visual tests are better suited for verifying appearance. Snapshot tests are useful for smoke testing and ensuring the DOM doesn’t change.

Learn about other UI tests

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