@blazediff/vitest

Vitest matcher for visual regression testing with blazediff. Provides native toMatchImageSnapshot() matcher with automatic snapshot state tracking and support for multiple comparison algorithms.

Installation


npm install --save-dev @blazediff/vitest


pnpm add --save-dev @blazediff/vitest


yarn add --dev @blazediff/vitest


bun add --dev @blazediff/vitest

Peer dependencies: Vitest >= 1.0.0

Features

Native Vitest matcher: toMatchImageSnapshot() extends Vitest’s expect API
Snapshot state tracking: Accurate snapshot counts in Vitest’s test summary
Multiple algorithms: Choose from 6 comparison methods
Auto-setup: Imports and registers automatically
Update mode: Works seamlessly with Vitest’s -u flag
Full TypeScript support: Complete type definitions included

Quick Start


import { expect, it } from 'vitest';
import '@blazediff/vitest';
 
it('should match screenshot', async () => {
  const screenshot = await page.screenshot();
 
  await expect(screenshot).toMatchImageSnapshot({
    method: 'core',
  });
});

The matcher auto-registers when you import @blazediff/vitest. No additional setup required!

API Reference

toMatchImageSnapshot(options?)

Vitest matcher for image snapshot comparison.


await expect(imageInput).toMatchImageSnapshot(options?);

Parameters

Parameter	Type	Description
`imageInput`	`ImageInput`	Image to compare (file path or buffer with dimensions)
`options`	`Partial<MatcherOptions>`	Optional comparison options

Options

Option	Type	Default	Description
`method`	`ComparisonMethod`	`'core'`	Comparison algorithm
`failureThreshold`	`number`	`0`	Allowed difference (pixels or percentage)
`failureThresholdType`	`'pixel' \| 'percent'`	`'pixel'`	Threshold interpretation
`snapshotsDir`	`string`	`'__snapshots__'`	Snapshot directory (relative to test)
`snapshotIdentifier`	`string`	auto-generated	Custom snapshot filename
`updateSnapshots`	`boolean`	`false`	Force snapshot update
`threshold`	`number`	`0.1`	Color threshold for `core`/`bin` (0-1)

See @blazediff/matcher for all available options.

Comparison Methods

`core` - Pure JavaScript (Default)


await expect(screenshot).toMatchImageSnapshot({
  method: 'core', // Fast, works with buffers and file paths
});

`bin` - Rust Native (Fastest)


await expect('/path/to/image.png').toMatchImageSnapshot({
  method: 'bin', // Requires file paths
});

`ssim` - Perceptual Similarity


await expect(screenshot).toMatchImageSnapshot({
  method: 'ssim', // Structural similarity
});

`gmsd` - Gradient-based


await expect(screenshot).toMatchImageSnapshot({
  method: 'gmsd', // Detects structural changes
});

Usage Patterns

Basic Snapshot Test


import { expect, it } from 'vitest';
import '@blazediff/vitest';
 
it('renders homepage correctly', async () => {
  const screenshot = await browser.screenshot();
 
  await expect(screenshot).toMatchImageSnapshot({
    method: 'core',
  });
});

Custom Thresholds

Allow small differences while catching regressions:


// Allow up to 100 pixels difference
await expect(screenshot).toMatchImageSnapshot({
  method: 'core',
  failureThreshold: 100,
  failureThresholdType: 'pixel',
});
 
// Allow up to 0.5% difference
await expect(screenshot).toMatchImageSnapshot({
  method: 'core',
  failureThreshold: 0.5,
  failureThresholdType: 'percent',
});

Use percentage-based thresholds for responsive images that may change size across different viewports.

Update Snapshots


# Update all failing snapshots
vitest -u
 
# Update snapshots for specific test file
vitest -u src/components/Button.test.ts
 
# Update snapshots matching pattern
vitest -u --testNamePattern="renders correctly"
 
# Using environment variable
VITEST_UPDATE_SNAPSHOTS=true vitest

Programmatically:


await expect(screenshot).toMatchImageSnapshot({
  method: 'core',
  updateSnapshots: true,
});

Custom Snapshot Directory


await expect(screenshot).toMatchImageSnapshot({
  method: 'core',
  snapshotsDir: '__image_snapshots__', // Custom directory
});

Custom Snapshot Identifier


await expect(screenshot).toMatchImageSnapshot({
  method: 'core',
  snapshotIdentifier: 'homepage-desktop-1920x1080',
});

Negation

Test that images are intentionally different:


const before = await page.screenshot();
await page.click('.toggle-theme');
const after = await page.screenshot();
 
// Assert that theme toggle changed the UI
await expect(after).not.toMatchImageSnapshot({
  method: 'core',
  snapshotIdentifier: 'before-theme-toggle',
});

Sequential Tests

For tests that share state, use sequential execution:


import { describe, it } from 'vitest';
 
describe.sequential('Visual regression tests', () => {
  it('test 1', async () => {
    await expect(image1).toMatchImageSnapshot({ method: 'core' });
  });
 
  it('test 2', async () => {
    await expect(image2).toMatchImageSnapshot({ method: 'core' });
  });
});

Integrations

Playwright


import { test, expect } from 'vitest';
import '@blazediff/vitest';
import { chromium } from 'playwright';
 
test('visual regression with Playwright', async () => {
  const browser = await chromium.launch();
  const page = await browser.newPage();
  await page.goto('https://example.com');
 
  const screenshot = await page.screenshot();
  await expect(screenshot).toMatchImageSnapshot({
    method: 'core',
  });
 
  await browser.close();
});

Puppeteer


import { test, expect } from 'vitest';
import '@blazediff/vitest';
import puppeteer from 'puppeteer';
 
test('captures homepage', async () => {
  const browser = await puppeteer.launch();
  const page = await browser.newPage();
  await page.goto('https://example.com');
 
  const screenshot = await page.screenshot({ fullPage: true });
 
  await expect(screenshot).toMatchImageSnapshot({
    method: 'core',
  });
 
  await browser.close();
});

React Testing Library


import { test, expect } from 'vitest';
import { render } from '@testing-library/react';
import '@blazediff/vitest';
import html2canvas from 'html2canvas';
 
test('renders button correctly', async () => {
  const { container } = render(<Button>Click me</Button>);
 
  const canvas = await html2canvas(container);
  const imageData = canvas.toDataURL();
 
  await expect(imageData).toMatchImageSnapshot({
    method: 'core',
  });
});

Snapshot State Tracking

The matcher integrates with Vitest’s snapshot state system. Test summaries show accurate counts:


Snapshots  2 written | 1 updated | 5 passed

Tracked states:

Written: New snapshots created
Updated: Snapshots updated with -u flag
Passed: Existing snapshots matched
Failed: Comparisons failed (shown in test results)

TypeScript

Full TypeScript support is included:


import { expect, it } from 'vitest';
import '@blazediff/vitest';
 
// Types are automatically augmented
it('typed test', async () => {
  const screenshot: Buffer = await takeScreenshot();
 
  await expect(screenshot).toMatchImageSnapshot({
    method: 'core',
    failureThreshold: 0.1,
    failureThresholdType: 'percent',
  });
});

The type augmentation is automatic when you import the package.

Configuration

Global Setup

To avoid importing in every test file, configure Vitest:


// vitest.config.ts
import { defineConfig } from 'vitest/config';
 
export default defineConfig({
  test: {
    setupFiles: ['./vitest.setup.ts'],
  },
});


// vitest.setup.ts
import '@blazediff/vitest';

Default Options

Create a wrapper to set default options:


// test-utils.ts
import { expect } from 'vitest';
import type { MatcherOptions } from '@blazediff/matcher';
 
export async function expectImageSnapshot(
  image: any,
  options?: Partial<MatcherOptions>
) {
  return expect(image).toMatchImageSnapshot({
    method: 'core',
    failureThreshold: 0.1,
    failureThresholdType: 'percent',
    ...options,
  });
}


// test.spec.ts
import { expectImageSnapshot } from './test-utils';
 
it('uses default options', async () => {
  await expectImageSnapshot(screenshot);
});

Watch Mode

Vitest’s watch mode works seamlessly with image snapshots:


# Start in watch mode
vitest --watch
 
# Update snapshots in watch mode
# Press 'u' in the terminal when prompted

In watch mode, Vitest will prompt you to update snapshots when they fail. Press u to update all failing snapshots.

Troubleshooting

Snapshots Not Updating

Ensure you’re using the -u flag:


vitest -u

Or set updateSnapshots: true in options.

Type Errors

Make sure @blazediff/vitest is imported:


import '@blazediff/vitest';

Snapshot Directory Not Found

The matcher creates directories automatically. If you see errors, check file permissions or specify an absolute path:


await expect(screenshot).toMatchImageSnapshot({
  method: 'core',
  snapshotsDir: '/absolute/path/to/snapshots',
});

Worker Thread Issues

If you encounter issues with Vitest’s worker threads, ensure you’re using the latest version:


npm update vitest