storybook-addon-vis

Storybook Vitest Image Snapshot add-on.

Captures and compare image snapshot automatically and manually.

This add-on is inspired by jest-image-snapshot.

Starting from storybook 8.3, you can run Storybook stories with vitest browser mode.

Since it is running in actual browser, jest-image-snapshot does not work. This add-on provides similar functionality to jest-image-snapshot. In addition, you can capture image snapshot manually.

Install

npm install --save-dev storybook-addon-vis

pnpm add --save-dev storybook-addon-vis

yarn add --save-dev storybook-addon-vis

Config

This add-on provides features on both storybook and vitest, thus you need to add it to both storybook and vitest.

On vitest, you need to add storybook-addon-vis/vitest-plugin plugin in vitest.config.ts.

// vite.config.ts or vitest.config.ts
import { storybookTest } from '@storybook/experimental-addon-test/vitest-plugin'
import { storybookVis } from 'storybook-addon-vis/vitest-plugin'
import { defineConfig } from 'vitest/config'

export default defineConfig({
    plugins: [
        storybookTest(),
        storybookVis()
    ],
    test: {
        browser: {
            // ...
        },
        global: false, // recommend to set to false
        setupFiles: ['./vitest.setup.ts'],
    }
})

Note that we recommend to set global to false. Setting global to true actually works ok during test, although you need to access the functions from the globalThis or window object is the story files.

However, the problem is when the story is run within storybook. In storybook, the global field has no effect. And in fact, you need to import the functions from @storybook/test instead:

// some.test.ts
import { expect } from 'vitest'

// some.stories.ts
import { expect } from '@storybook/test'

Therefore, the story will crash when run in storybook because those functions are undefined.

In vitest.setup.ts, you can use one of the presets to do the setup for you. You can also use the provided hooks to set up the test environment manually.

// vitest.setup.ts
import { setProjectAnnotations } from '@storybook/react'
import { createVisConfig } from 'storybook-addon-vis/vitest-setup'
import * as projectAnnotations from './preview'

const project = setProjectAnnotations([projectAnnotations])

// capture image snapshot for all stories with `snapshot` tag
createVisConfig(/* options */).presets.basic()

// capture image snapshot for all stories with `snapshot` tag,
// for both light and dark themes
createVisConfig(/* options */).presets.theme({
    light() { document.body.classList.remove('dark') },
    dark() { document.body.classList.add('dark') },
})

On storybook, you need to register the beforeEach hook in .storybook/preview.ts.

// .storybook/preview.tsx
import { storybookPreviewVis } from 'storybook-addon-vis'

export default {
    // ...
    beforeEach: storybookPreviewVis.beforeEach
}

Usage - automatic snapshot

With the basic preset, storybook-addon-vis automatically captures image snapshot for stories with snapshot tag.

As with how tags work in storybook, you can add the tag globally, per story file, or per story.

// .storybook/preview.tsx
export default {
    // Enable image snapshot for all stories
    tags: ['snapshot']
}

// story.tsx
export default {
    title: 'Button',
    // Take image snapshot automatically for all stories in this file
    tags: ['snapshot']
}

export const MyStory = {
    // Take image snapshot automatically for this story
    tags: ['snapshot'],
    // ...
}

You can disable snapshot capturing with the !snapshot tag, much like !test.

export default {
    title: 'Button',
    // Enable image snapshot for all stories in this file
    tags: ['snapshot']
}

export const MyStory = {
    // Disable image snapshot for this story
    tags: ['!snapshot'],
    // ...
}

You can provide options to the toMatchImageSnapshot matcher using parameters.

import { defineSnapshotParam } from 'storybook-addon-vis'

export const MyStory = {
    parameters: defineSnapshotParam({
        failureThreshold: 70,
    })
    // ...
}

Usage - manual snapshot

Besides automatic snapshot, you can capture image snapshot manually.

import { expect } from '@storybook/test'

// `page` and the like are proxies of `@vitest/browser/context` to work within storybook
import { page } from 'storybook-addon-vis'

export const PageSnapshot = {
    // typically you want to disable automatic snapshot when using manual snapshot
    tags: ['!snapshot'],
    // ...
    async play() {
        await expect(page.imageSnapshot()).toMatchImageSnapshot()
    }
}

export const ElementSnapshot = {
    // typically you want to disable automatic snapshot when using manual snapshot
    tags: ['!snapshot'],
    // ...
    async play({ canvas }) {
        const element = await canvas.getByTestid('subject')
        await expect(page.imageSnapshot({ element })).toMatchImageSnapshot()
    }
}

Snapshot folder

By default, the snapshots are stored under the __vis__ folder at the root of the project:

v __vis__
    ˃ __diff_output__ # where the diff images are stored
    ˃ __result__ # where the resulting snapshot of the current run are stored
    ˃ darwin # snapshot generated on macos by CI
    ˃ linux # snapshot generated on linux by CI
    v local # snapshot generated on local machine
        v button.stories.tsx
            snapshot-1.png
            snapshot-2.png
v src
    button.stories.tsx

You can change the snapshot folder by providing the snapshotRootDir option to the createVisConfig function.

import { createVisConfig } from 'storybook-addon-vis/vitest-setup'

createVisConfig({
    snapshotRootDir: 'path/to/snapshot'
})

Typically, you place your test files either in a dedicated tests folder or in the src folder along with your source code. By default, storybook-addon-vis removes that folder to reduces nesting.

If you place your test files in multiple folders, such as in both tests and src folders, you can use customizeSnapshotSubpath to customize the snapshot sub-path to avoid conflicts.

import { createVisConfig } from 'storybook-addon-vis/vitest-setup'

createVisConfig({
    // keep the folder structure
    customizeSnapshotSubpath: (subpath) => subpath
})

With the above configuration, the snapshot folder structure will look like this:

v __vis__
    > # ...
    v local # snapshot generated on local machine
        v examples
            v button.stories.tsx
                snapshot-1.png
                snapshot-2.png
        v src
            v button.stories.tsx
                snapshot-1.png
                snapshot-2.png
        v tests
            v button.stories.tsx
                snapshot-1.png
                snapshot-2.png
v examples
    button.stories.tsx
v src
    button.stories.tsx
v tests
    button.stories.tsx

Ignore snapshot folders

Some snapshot folders should be ignored by git.

With the default snapshot folder structure, you should add the following to your .gitignore:

# .gitignore
**/__vis__/__diff_output__
**/__vis__/__results__
**/__vis__/local

Troubleshooting

Internal server error: Failed to resolve import "pathe"

This is likely a compatibility issue with pnpm and vite in monorepo.

To work around this, you can add shamefully-hoist to your .npmrc:

# .npmrc

shamefully-hoist=true