Agent skill

bun-test-lifecycle

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Install this agent skill to your Project

npx add-skill https://github.com/secondsky/claude-skills/tree/main/plugins/bun/skills/bun-test-lifecycle

SKILL.md

Bun Test Lifecycle

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

Lifecycle Hooks

typescript
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

typescript
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

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

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

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

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

Timeout for Hooks

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

Preload Scripts

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

bash
bun test --preload ./setup.ts

setup.ts

typescript
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

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

Common Patterns

Database Setup

typescript
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

typescript
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}`;
});

afterAll(() => {
  server.stop();
});

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

Mock Setup

typescript
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

typescript
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

typescript
// 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:

typescript
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

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