Bun Test Lifecycle

Bun supports Jest-compatible lifecycle hooks for test setup and teardown.

Lifecycle Hooks

import { test, expect, beforeAll, afterAll, beforeEach, afterEach } from "bun:test";

let db: Database;
let testData: any;

// Runs once before all tests in file
beforeAll(async () => {
  db = await Database.connect();
});

// Runs once after all tests in file
afterAll(async () => {
  await db.close();
});

// Runs before each test
beforeEach(() => {
  testData = { id: 1, name: "test" };
});

// Runs after each test
afterEach(() => {
  testData = null;
});

test("example", () => {
  expect(testData.name).toBe("test");
});

Hook Execution Order

beforeAll
  ├── beforeEach
  │   └── test 1
  │   └── afterEach
  ├── beforeEach
  │   └── test 2
  │   └── afterEach
afterAll

Nested Describe Hooks

import { describe, test, beforeAll, beforeEach, afterEach, afterAll } from "bun:test";

describe("outer", () => {
  beforeAll(() => console.log("1. outer beforeAll"));
  afterAll(() => console.log("6. outer afterAll"));
  beforeEach(() => console.log("2. outer beforeEach"));
  afterEach(() => console.log("5. outer afterEach"));

  describe("inner", () => {
    beforeEach(() => console.log("3. inner beforeEach"));
    afterEach(() => console.log("4. inner afterEach"));

    test("test", () => {
      console.log("test runs here");
    });
  });
});

// Output:
// 1. outer beforeAll
// 2. outer beforeEach
// 3. inner beforeEach
// test runs here
// 4. inner afterEach
// 5. outer afterEach
// 6. outer afterAll

Async Hooks

beforeAll(async () => {
  await setupDatabase();
});

beforeEach(async () => {
  await seedTestData();
});

afterEach(async () => {
  await clearTestData();
});

afterAll(async () => {
  await teardownDatabase();
});

Timeout for Hooks

// Set timeout for slow setup
beforeAll(async () => {
  await slowSetup();
}, 30000); // 30 seconds

Preload Scripts

Use --preload for global setup across all test files:

bun test --preload ./setup.ts

setup.ts

import { beforeAll, afterAll } from "bun:test";

// Global setup
beforeAll(() => {
  console.log("Global setup runs before all test files");
});

// Global teardown
afterAll(() => {
  console.log("Global teardown runs after all test files");
});

// Set global variables
globalThis.testConfig = {
  apiUrl: "http://localhost:3000",
};

Configure in bunfig.toml

[test]
preload = ["./test/setup.ts"]

Common Patterns

Database Setup

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

let db: Database;

beforeAll(async () => {
  db = await Database.connect(process.env.TEST_DB_URL);
  await db.migrate();
});

afterAll(async () => {
  await db.close();
});

beforeEach(async () => {
  await db.beginTransaction();
});

afterEach(async () => {
  await db.rollback(); // Reset state
});

Server Setup

import { beforeAll, afterAll } from "bun:test";

let server: Server;
let baseUrl: string;

beforeAll(async () => {
  server = Bun.serve({
    port: 0, // Random available port
    fetch: app.fetch,
  });
  baseUrl = `http://localhost:${server.port}`;
});

// Bun 1.2+: server.stop() returns a Promise that resolves once in-flight
// connections have closed — await it so the test process doesn't exit early.
afterAll(async () => {
  await server.stop();
});

test("api works", async () => {
  const res = await fetch(`${baseUrl}/api/health`);
  expect(res.ok).toBe(true);
});

Mock Setup

import { beforeEach, afterEach, spyOn } from "bun:test";

let fetchSpy: ReturnType<typeof spyOn>;

beforeEach(() => {
  fetchSpy = spyOn(global, "fetch").mockResolvedValue(
    new Response(JSON.stringify({ ok: true }))
  );
});

afterEach(() => {
  fetchSpy.mockRestore();
});

Environment Variables

import { beforeAll, afterAll } from "bun:test";

const originalEnv = process.env;

beforeAll(() => {
  process.env = {
    ...originalEnv,
    NODE_ENV: "test",
    API_KEY: "test-key",
  };
});

afterAll(() => {
  process.env = originalEnv;
});

Shared Fixtures

// fixtures.ts
export async function createTestUser() {
  return { id: 1, name: "Test User" };
}

export async function cleanupTestUser(user: any) {
  // cleanup logic
}

// test file
import { createTestUser, cleanupTestUser } from "./fixtures";

let user: any;

beforeEach(async () => {
  user = await createTestUser();
});

afterEach(async () => {
  await cleanupTestUser(user);
});

Hook Errors

If a hook throws, all tests in that describe block fail:

beforeAll(() => {
  throw new Error("Setup failed");
});

// All tests in this file will fail
test("will fail", () => {
  expect(true).toBe(true);
});

Common Errors

Error	Cause	Fix
beforeAll timeout	Slow async setup	Increase timeout
Hook not called	Wrong scope	Check hook placement
Cleanup not run	afterAll skipped	Ensure no throws in tests
State leak	Missing cleanup	Add proper afterEach

When to Load References

Load references/preload-scripts.md when:

• Complex global setup
• Multiple preload files

Load references/fixtures.md when:

• Reusable test fixtures
• Factory patterns