jarle/Bun Lifecycle hooks

Lifecycle hooks

Learn how to use beforeAll, beforeEach, afterEach, and afterAll lifecycle hooks in Bun tests

The test runner supports the following lifecycle hooks. This is useful for loading test fixtures, mocking data, and configuring the test environment.

| Hook | Description | | ---------------- | ---------------------------------------------------------- | | beforeAll | Runs once before all tests. | | beforeEach | Runs before each test. | | afterEach | Runs after each test. | | afterAll | Runs once after all tests. | | onTestFinished | Runs after a single test finishes (after all afterEach). |

Per-Test Setup and Teardown

Perform per-test setup and teardown logic with beforeEach and afterEach.

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

beforeEach(() => {
  console.log("running test.");
});

afterEach(() => {
  console.log("done with test.");
});

// tests...
test("example test", () => {
  // This test will have beforeEach run before it
  // and afterEach run after it
});

Per-Scope Setup and Teardown

Perform per-scope setup and teardown logic with beforeAll and afterAll. The scope is determined by where the hook is defined.

Scoped to a Describe Block

To scope the hooks to a particular describe block:

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

describe("test group", () => {
  beforeAll(() => {
    // setup for this describe block
    console.log("Setting up test group");
  });

  afterAll(() => {
    // teardown for this describe block
    console.log("Tearing down test group");
  });

  test("test 1", () => {
    // test implementation
  });

  test("test 2", () => {
    // test implementation
  });
});

Scoped to a Test File

To scope the hooks to an entire test file:

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

beforeAll(() => {
  // setup for entire file
  console.log("Setting up test file");
});

afterAll(() => {
  // teardown for entire file
  console.log("Tearing down test file");
});

describe("test group", () => {
  test("test 1", () => {
    // test implementation
  });
});

onTestFinished

Use onTestFinished to run a callback after a single test completes. It runs after all afterEach hooks.

import { test, onTestFinished } from "bun:test";

test("cleanup after test", () => {
  onTestFinished(() => {
    // runs after all afterEach hooks
    console.log("test finished");
  });
});

Not supported in concurrent tests; use test.serial instead.

Global Setup and Teardown

To scope the hooks to an entire multi-file test run, define the hooks in a separate file.

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

beforeAll(() => {
  // global setup
  console.log("Global test setup");
  // Initialize database connections, start servers, etc.
});

afterAll(() => {
  // global teardown
  console.log("Global test teardown");
  // Close database connections, stop servers, etc.
});

Then use --preload to run the setup script before any test files.

bun test --preload ./setup.ts

To avoid typing --preload every time you run tests, it can be added to your bunfig.toml:

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

Practical Examples

Database Setup

import { beforeAll, afterAll, beforeEach, afterEach } from "bun:test";
import { createConnection, closeConnection, clearDatabase } from "./db";

let connection;

beforeAll(async () => {
  // Connect to test database
  connection = await createConnection({
    host: "localhost",
    database: "test_db",
  });
});

afterAll(async () => {
  // Close database connection
  await closeConnection(connection);
});

beforeEach(async () => {
  // Start with clean database for each test
  await clearDatabase(connection);
});

API Server Setup

import { beforeAll, afterAll } from "bun:test";
import { startServer, stopServer } from "./server";

let server;

beforeAll(async () => {
  // Start test server
  server = await startServer({
    port: 3001,
    env: "test",
  });
});

afterAll(async () => {
  // Stop test server
  await stopServer(server);
});

Mock Setup

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

beforeEach(() => {
  // Set up common mocks
  mock.module("./api-client", () => ({
    fetchUser: mock(() => Promise.resolve({ id: 1, name: "Test User" })),
    createUser: mock(() => Promise.resolve({ id: 2 })),
  }));
});

afterEach(() => {
  // Clear all mocks after each test
  mock.restore();
});

Async Lifecycle Hooks

All lifecycle hooks support async functions:

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

beforeAll(async () => {
  // Async setup
  await new Promise(resolve => setTimeout(resolve, 100));
  console.log("Async setup complete");
});

afterAll(async () => {
  // Async teardown
  await new Promise(resolve => setTimeout(resolve, 100));
  console.log("Async teardown complete");
});

test("async test", async () => {
  // Test will wait for beforeAll to complete
  await expect(Promise.resolve("test")).resolves.toBe("test");
});

Nested Hooks

Hooks can be nested and will run in the appropriate order:

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

beforeAll(() => console.log("File beforeAll"));
afterAll(() => console.log("File afterAll"));

describe("outer describe", () => {
  beforeAll(() => console.log("Outer beforeAll"));
  beforeEach(() => console.log("Outer beforeEach"));
  afterEach(() => console.log("Outer afterEach"));
  afterAll(() => console.log("Outer afterAll"));

  describe("inner describe", () => {
    beforeAll(() => console.log("Inner beforeAll"));
    beforeEach(() => console.log("Inner beforeEach"));
    afterEach(() => console.log("Inner afterEach"));
    afterAll(() => console.log("Inner afterAll"));

    test("nested test", () => {
      console.log("Test running");
    });
  });
});

// Output order:
// File beforeAll
// Outer beforeAll
// Inner beforeAll
// Outer beforeEach
// Inner beforeEach
// Test running
// Inner afterEach
// Outer afterEach
// Inner afterAll
// Outer afterAll
// File afterAll

Error Handling

If a lifecycle hook throws an error, it will affect test execution:

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

beforeAll(() => {
  // If this throws, all tests in this scope will be skipped
  throw new Error("Setup failed");
});

test("this test will be skipped", () => {
  // This won't run because beforeAll failed
});

For better error handling:

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

beforeAll(async () => {
  try {
    await setupDatabase();
  } catch (error) {
    console.error("Database setup failed:", error);
    throw error; // Re-throw to fail the test suite
  }
});

Best Practices

Keep Hooks Simple

// Good: Simple, focused setup
beforeEach(() => {
  clearLocalStorage();
  resetMocks();
});

// Avoid: Complex logic in hooks
beforeEach(async () => {
  // Too much complex logic makes tests hard to debug
  const data = await fetchComplexData();
  await processData(data);
  await setupMultipleServices(data);
});

Use Appropriate Scope

// Good: File-level setup for shared resources
beforeAll(async () => {
  await startTestServer();
});

// Good: Test-level setup for test-specific state
beforeEach(() => {
  user = createTestUser();
});

Clean Up Resources

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

afterEach(() => {
  // Clean up after each test
  document.body.innerHTML = "";
  localStorage.clear();
});

afterAll(async () => {
  // Clean up expensive resources
  await closeDatabase();
  await stopServer();
});