Bun Testing

Bun Testing Skill

Quick Reference

• Framework: bun:test
• File pattern: *.test.ts inside __tests__ directories
• Module mocking: Use ModuleMocker from @/__tests__ (see patterns)
• Coverage target: 60–80% (focus on important logic, not 100%)
• Config: .env.test for test environment variables

Test Utilities (src/tests/)

Before writing custom test helpers, check existing utilities:

• createTestApp(basePath, route, middleware[]) - Creates test Hono app with error handler, logger, and optional middleware
• ModuleMocker(import.meta.url) - Module mocking utility (see mocking patterns)
• post(app, url, body, headers) - POST request helper
• get(app, url, headers) - GET request helper
• doRequest(app, url, method, body, headers) - Generic request helper

Example:

import { createTestApp, post } from '@/__tests__'

const app = createTestApp('/api/v1/auth', signupRoute, [captchaMiddleware()])
const response = await post(app, '/api/v1/auth/signup', {
  email: 'test@example.com',
  password: 'SecurePass123!'
})

Test Types

• Unit tests: Mock all dependencies (repositories, services, APIs)
• Integration tests: Use real database, mock external APIs only
• Endpoint tests: Use createTestApp() with mocked services

Test Priorities

1. Correct scenario(s)
2. Error handling
3. Boundary inputs
4. Failure scenarios

Environment Setup

• Use .env.test for test-specific variables
• Bun handles env loading natively — no manual dotenv needed
• Minimize mocking @/env — only mock for special/invalid configs

Mocking Strategy

• Mock only business logic dependencies (repositories, external APIs)
• Use global mocks for shared services (CAPTCHA, email) — don't redefine per test
• No real database or network calls — all I/O must be mocked
• Don't mock encapsulated dependencies — mock the public API/wrapper only

Type Safety

• Minimize any — prefer proper TypeScript types
• Use type inference when possible
• Use Partial<T> for mock objects
• Exception: Use any only for complex mocks where full typing adds unnecessary complexity

Test Structure

Use arrange → act → assert pattern with descriptive test names:

describe('UserService', () => {
  it('should return user when found by email', async () => {
    // Arrange
    const mockUser = { id: 1, email: 'test@example.com' }
    mockUserRepo.findByEmail.mockResolvedValue(mockUser)

    // Act
    const result = await userService.findByEmail('test@example.com')

    // Assert
    expect(result).toEqual(mockUser)
  })
})

Mocking Patterns

For detailed mocking patterns including variable ordering, beforeEach setup, and ModuleMocker usage, see references/mocking-patterns.md.

Cleanup

Always clean up side effects after each test:

afterEach(async () => {
  await moduleMocker.clear() // restore mocked modules
  vi.clearAllMocks() // or mock.mockClear() for individual mocks
})