@blazediff/bun

toMatchImageSnapshot() for Bun. Auto-registers on import, supports all comparison methods.

Installation


npm install --save-dev @blazediff/bun


pnpm add --save-dev @blazediff/bun


yarn add --dev @blazediff/bun


bun add --dev @blazediff/bun

Peer dependencies: Bun >= 1.0.0

Quick Start


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

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

Unlike Jest/Vitest, Bun has limited context exposure. Always provide a snapshotIdentifier for reliable snapshot management.

API Reference

toMatchImageSnapshot(options?)

Bun test 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
`snapshotIdentifier`	`string`	`'snapshot'`	Required: Snapshot filename identifier
`failureThreshold`	`number`	`0`	Allowed difference (pixels or percentage)
`failureThresholdType`	`'pixel' \| 'percent'`	`'pixel'`	Threshold interpretation
`snapshotsDir`	`string`	`'__snapshots__'`	Snapshot directory (relative to test)
`updateSnapshots`	`boolean`	`false`	Force snapshot update
`threshold`	`number`	`0.1`	Color threshold for `core`/`core-native` (0-1)
`runInWorker`	`boolean`	`true`	Run comparison in worker thread for better performance

See @blazediff/matcher for all available options.

Comparison Methods

`core` - Pure JavaScript (Default)


await expect(screenshot).toMatchImageSnapshot({
  method: 'core',
  snapshotIdentifier: 'my-test',
});

`core-native` - Rust Native (Fastest)


await expect('/path/to/image.png').toMatchImageSnapshot({
  method: 'core-native',
  snapshotIdentifier: 'my-test',
});

`ssim` - Perceptual Similarity


await expect(screenshot).toMatchImageSnapshot({
  method: 'ssim',
  snapshotIdentifier: 'my-test',
});

`gmsd` - Gradient-based


await expect(screenshot).toMatchImageSnapshot({
  method: 'gmsd',
  snapshotIdentifier: 'my-test',
});

Usage Patterns

Basic Snapshot Test


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

Custom Thresholds

Allow small differences while catching regressions:


// Allow up to 100 pixels difference
await expect(screenshot).toMatchImageSnapshot({
  method: 'core',
  snapshotIdentifier: 'homepage',
  failureThreshold: 100,
  failureThresholdType: 'pixel',
});
 
// Allow up to 0.5% difference
await expect(screenshot).toMatchImageSnapshot({
  method: 'core',
  snapshotIdentifier: 'homepage',
  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 (recommended)
bun test --update-snapshots
 
# Using environment variable
BUN_UPDATE_SNAPSHOTS=true bun test

The Bun’s --update-snapshots flag is consumed by Bun internally and won’t update image snapshots.

Programmatically:


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

Custom Snapshot Directory


await expect(screenshot).toMatchImageSnapshot({
  method: 'core',
  snapshotIdentifier: 'homepage',
  snapshotsDir: '__image_snapshots__',
});

Bun-Specific Notes

Unlike Jest and Vitest, Bun has limited test context exposure. Always provide a snapshotIdentifier:


// Good
await expect(screenshot).toMatchImageSnapshot({
  method: 'core',
  snapshotIdentifier: 'my-component',
});
 
// Avoid - falls back to generic "snapshot"
await expect(screenshot).toMatchImageSnapshot({
  method: 'core',
});