bun-test

name	bun-test
description	Configure Bun's built-in test runner with Jest-compatible APIs. Use when setting up testing infrastructure, writing unit/integration/snapshot tests, migrating from Jest, or configuring test coverage. 3-10x faster than Jest.
compatibility	Requires Bun 1.0+
allowed-tools	["Bash","Write","Read"]
metadata	{"author":"dale","category":"bun-runtime","tags":["bun","testing","jest","unit-tests","tdd"]}

Bun Test Configuration

Set up Bun's built-in test runner with Jest-compatible APIs and significantly faster execution (3-10x faster than Jest).

Quick Reference

For detailed patterns, see:

• Jest Migration: jest-migration.md - Complete Jest to Bun migration guide
• Mocking: mocking.md - Mock functions, spies, module mocking
• Examples: examples.md - Test patterns for APIs, databases, async code

Core Workflow

1. Check Prerequisites

# Verify Bun installation
bun --version

# Check if project exists
ls -la package.json

2. Determine Testing Needs

Ask the user what type of testing they need:

• Unit Testing: Test individual functions and modules
• Integration Testing: Test component interactions
• API Testing: Test HTTP endpoints
• Snapshot Testing: Test output consistency

3. Create Test Directory Structure

# Create test directories
mkdir -p tests/{unit,integration,fixtures}

Recommended structure:

project/
├── src/
│   ├── utils.ts
│   └── components/
├── tests/
│   ├── unit/              # Unit tests
│   ├── integration/       # Integration tests
│   ├── fixtures/          # Test data
│   └── setup.ts          # Global setup
├── package.json
└── bunfig.toml           # Test configuration

4. Configure Bun Test

Create bunfig.toml in project root:

[test]
# Preload files before running tests
preload = ["./tests/setup.ts"]

# Code coverage
coverage = true
coverageDir = "coverage"
coverageThreshold = 80

# Timeouts (in milliseconds)
timeout = 5000

# Bail after first failure
bail = false

5. Create Test Setup File

Create tests/setup.ts:

import {beforeAll, afterAll, beforeEach, afterEach} from 'bun:test'

// Global test setup
beforeAll(() => {
	console.log('🧪 Starting test suite')
	process.env.NODE_ENV = 'test'
})

afterAll(() => {
	console.log('✅ Test suite complete')
})

// Reset mocks before each test
beforeEach(() => {
	// Clear mock state
})

afterEach(() => {
	// Cleanup after each test
})

// Global test utilities
globalThis.testHelpers = {
	wait: (ms: number) => new Promise(resolve => setTimeout(resolve, ms)),
}

6. Write First Test

Create tests/unit/example.test.ts:

import {describe, it, expect, test} from 'bun:test'

// Simple test
test('addition works', () => {
	expect(1 + 1).toBe(2)
})

// Describe blocks for organization
describe('Array utilities', () => {
	it('should filter even numbers', () => {
		const numbers = [1, 2, 3, 4, 5, 6]
		const evens = numbers.filter(n => n % 2 === 0)

		expect(evens).toEqual([2, 4, 6])
		expect(evens).toHaveLength(3)
	})
})

// Async tests
describe('Async operations', () => {
	it('should handle promises', async () => {
		const result = await Promise.resolve(42)
		expect(result).toBe(42)
	})
})

For more test examples (API testing, database testing, etc.), see examples.md.

7. Add Mocking (If Needed)

import {describe, it, expect, mock, spyOn} from 'bun:test'

describe('Mock functions', () => {
	it('should create mock functions', () => {
		const mockFn = mock((x: number) => x * 2)

		const result = mockFn(5)

		expect(result).toBe(10)
		expect(mockFn).toHaveBeenCalledTimes(1)
		expect(mockFn).toHaveBeenCalledWith(5)
	})

	it('should spy on methods', () => {
		const obj = {
			method: (x: number) => x * 2,
		}

		const spy = spyOn(obj, 'method')

		obj.method(5)

		expect(spy).toHaveBeenCalledWith(5)
		expect(spy).toHaveReturnedWith(10)
	})
})

For advanced mocking patterns, see mocking.md.

8. Update package.json

Add test scripts:

{
	"scripts": {
		"test": "bun test",
		"test:watch": "bun test --watch",
		"test:coverage": "bun test --coverage",
		"test:ui": "bun test --coverage --reporter=html"
	}
}

9. Run Tests

# Run all tests
bun test

# Run specific file
bun test tests/unit/utils.test.ts

# Watch mode
bun test --watch

# With coverage
bun test --coverage

# Filter by name
bun test --test-name-pattern="should handle"

Jest Migration

If migrating from Jest, see jest-migration.md for:

• Import updates (@jest/globals → bun:test)
• Mock syntax changes (jest.fn() → mock())
• Configuration migration
• Compatibility notes

Key changes:

// Before (Jest)
import {describe, it, expect} from '@jest/globals'
const mockFn = jest.fn()

// After (Bun)
import {describe, it, expect, mock} from 'bun:test'
const mockFn = mock()

Common Test Patterns

Testing Functions

import {test, expect} from 'bun:test'

function add(a: number, b: number): number {
	return a + b
}

test('add function', () => {
	expect(add(2, 3)).toBe(5)
	expect(add(-1, 1)).toBe(0)
})

Testing Errors

test('should throw errors', () => {
	const throwError = () => {
		throw new Error('Something went wrong')
	}

	expect(throwError).toThrow('Something went wrong')
	expect(throwError).toThrow(Error)
})

test('should reject promises', async () => {
	const asyncReject = async () => {
		throw new Error('Async error')
	}

	await expect(asyncReject()).rejects.toThrow('Async error')
})

Snapshot Testing

test('should match snapshot', () => {
	const data = {
		id: 1,
		name: 'Test User',
		email: '[e-mail]',
	}

	expect(data).toMatchSnapshot()
})

test('should match inline snapshot', () => {
	const config = {theme: 'dark', language: 'en'}

	expect(config).toMatchInlineSnapshot(`
    {
      "theme": "dark",
      "language": "en"
    }
  `)
})

Matchers Reference

Common matchers available:

// Equality
expect(value).toBe(expected) // ===
expect(value).toEqual(expected) // Deep equality

// Truthiness
expect(value).toBeTruthy()
expect(value).toBeFalsy()
expect(value).toBeDefined()
expect(value).toBeUndefined()

// Numbers
expect(number).toBeGreaterThan(3)
expect(number).toBeLessThan(5)

// Strings
expect(string).toMatch(/pattern/)
expect(string).toContain('substring')

// Arrays
expect(array).toContain(item)
expect(array).toHaveLength(3)

// Objects
expect(object).toHaveProperty('key')
expect(object).toMatchObject({subset})

// Promises
await expect(promise).resolves.toBe(value)
await expect(promise).rejects.toThrow()

// Mock functions
expect(mockFn).toHaveBeenCalled()
expect(mockFn).toHaveBeenCalledTimes(3)
expect(mockFn).toHaveBeenCalledWith(arg1, arg2)

Test Organization

Setup and Teardown

import {
	beforeAll,
	afterAll,
	beforeEach,
	afterEach,
	describe,
	it,
} from 'bun:test'

describe('User service', () => {
	let db: Database

	beforeAll(async () => {
		// Setup before all tests
		db = await connectToDatabase()
	})

	afterAll(async () => {
		// Cleanup after all tests
		await db.close()
	})

	beforeEach(async () => {
		// Reset before each test
		await db.clear()
	})

	it('should create user', async () => {
		const user = await db.users.create({name: 'Test'})
		expect(user.id).toBeDefined()
	})
})

Coverage Configuration

View coverage report:

# Generate coverage
bun test --coverage

# View HTML report
bun test --coverage --reporter=html
open coverage/index.html

Set coverage thresholds in bunfig.toml:

[test]
coverage = true
coverageThreshold = 80 # Fail if coverage < 80%

Debugging Tests

# Run with debugger
bun test --inspect

# Verbose output
bun test --verbose

# Show all test results
bun test --reporter=tap

Performance

Bun test is significantly faster than Jest:

• Jest: ~15 seconds for 100 tests
• Bun: ~2 seconds for 100 tests

3-10x faster execution!

Completion Checklist

• ✅ Test directory structure created
• ✅ bunfig.toml configured
• ✅ Test setup file created
• ✅ Example tests written
• ✅ Package.json scripts updated
• ✅ Tests run successfully
• ✅ Coverage configured (if needed)

Next Steps

After basic setup:

1. Write tests: Add tests for critical business logic
2. CI/CD: Configure tests to run in your pipeline
3. Coverage: Set up coverage reporting
4. Pre-commit: Add pre-commit hooks to run tests
5. Documentation: Document testing patterns for the team

For detailed implementations, see the reference files linked above.