Setup

Instalasi

npm install --save-dev jest
# package.json: "scripts": { "test": "jest" }
npx jest              # run all tests
npx jest --watch      # re-run on changes

Penamaan File

*.test.js	File test (pola default)
*.spec.js	Pola test alternatif
__tests__/	Direktori test (ditemukan otomatis)

Menjalankan Test Tertentu

npx jest path/to/file.test.js
npx jest --testNamePattern="adds"
npx jest --verbose     # detailed output

Test Dasar

Struktur Test

describe("Calculator", () => {
  test("adds 1 + 2 to equal 3", () => {
    expect(add(1, 2)).toBe(3);
  });
});

test vs it

test("works correctly", () => { /* ... */ });
it("should work correctly", () => { /* ... */ });
// Both are identical; "it" reads like English

Lewati & Fokus

test.skip()	Lewati test ini
test.only()	Jalankan hanya test ini
describe.skip()	Lewati seluruh suite
describe.only()	Jalankan hanya suite ini

Matcher

Kesamaan

.toBe(val)	Kesamaan ketat (`===`)
.toEqual(val)	Kesamaan mendalam (objek/array)
.toStrictEqual(val)	Mendalam + tipe + props undefined
.not.toBe(val)	Negasi matcher mana pun

Truthiness

.toBeTruthy()	Nilai truthy
.toBeFalsy()	Nilai falsy
.toBeNull()	Tepat `null`
.toBeUndefined()	Tepat `undefined`
.toBeDefined()	Bukan `undefined`

Angka

.toBeGreaterThan(n)	Lebih besar dari n
.toBeLessThanOrEqual(n)	Kurang dari atau sama dengan
.toBeCloseTo(0.3, 5)	Perbandingan float (5 digit)

String, Array, Objek

.toMatch(/regex/)	String cocok dengan regex
.toContain(item)	Array/iterable mengandung item
.toHaveLength(n)	Panjang array/string
.toHaveProperty(key, val)	Objek memiliki properti
.toMatchObject(obj)	Objek mengandung subset

Test Async

async / await

test("fetches data", async () => {
  const data = await fetchData();
  expect(data).toEqual({ id: 1 });
});

Promise

test("resolves to data", () => {
  return expect(fetchData())
    .resolves.toEqual({ id: 1 });
});

Rejection

test("rejects with error", async () => {
  await expect(fetchBad())
    .rejects.toThrow("Not Found");
});

Exception

test("throws on invalid input", () => {
  expect(() => validate(null)).toThrow();
  expect(() => validate(null)).toThrow("invalid");
});

Mocking

Fungsi Mock

const fn = jest.fn();
fn("hello");
expect(fn).toHaveBeenCalledWith("hello");
expect(fn).toHaveBeenCalledTimes(1);

Nilai Kembalian Mock

const fn = jest.fn()
  .mockReturnValue(42)
  .mockReturnValueOnce(99);
fn(); // 99 (first call)
fn(); // 42 (subsequent)

Mocking Module

jest.mock("./api");
const { fetchUser } = require("./api");
fetchUser.mockResolvedValue({ name: "Alice" });

Matcher Mock

.toHaveBeenCalled()	Dipanggil setidaknya sekali
.toHaveBeenCalledTimes(n)	Dipanggil tepat n kali
.toHaveBeenCalledWith(args)	Dipanggil dengan argumen tertentu
.toHaveBeenLastCalledWith(args)	Panggilan terakhir dengan argumen ini

Spy

Memata-matai Method

const spy = jest.spyOn(Math, "random")
  .mockReturnValue(0.5);
expect(Math.random()).toBe(0.5);
spy.mockRestore();  // restore original

Memata-matai Method Objek

const obj = { greet: (n) => `Hi ${n}` };
const spy = jest.spyOn(obj, "greet");
obj.greet("Alice");
expect(spy).toHaveBeenCalledWith("Alice");

Snapshot

Snapshot Testing

test("renders correctly", () => {
  const tree = renderer.create().toJSON();
  expect(tree).toMatchSnapshot();
});

Inline Snapshot

test("formats name", () => {
  expect(formatName("alice"))
    .toMatchInlineSnapshot(`"Alice"`);
});

Memperbarui Snapshot

npx jest --updateSnapshot   # update all
npx jest --updateSnapshot --testNamePattern="renders"

Setup & Teardown

Hook Siklus Hidup

beforeAll(() => { /* once before all tests */ });
afterAll(() => { /* once after all tests */ });
beforeEach(() => { /* before each test */ });
afterEach(() => { /* after each test */ });

Scoping

describe("Database", () => {
  beforeEach(() => db.connect());
  afterEach(() => db.disconnect());
  test("reads data", () => { /* ... */ });
});

Hook di dalam describe hanya berlaku untuk blok tersebut

Konfigurasi

jest.config.js

module.exports = {
  testEnvironment: "node",
  coverageThreshold: {
    global: { branches: 80, lines: 80 }
  },
};

Opsi Umum

testEnvironment	`"node"` atau `"jsdom"` (DOM)
roots	Direktori untuk mencari test
collectCoverage	Aktifkan pelaporan coverage
coverageDirectory	Direktori output untuk coverage
moduleNameMapper	Alias path (mis. prefiks `@/`)
transform	Transformasi file (Babel, TS, dll.)
setupFilesAfterFramework	Jalankan setup sebelum setiap suite

Coverage

npx jest --coverage
npx jest --collectCoverageFrom="src/**/*.js"

Pola Umum

Testing Panggilan API

jest.mock("./api");
test("loads users", async () => {
  api.getUsers.mockResolvedValue([{id: 1}]);
  const users = await loadUsers();
  expect(users).toHaveLength(1);
});

Mock Timer

jest.useFakeTimers();
test("delays execution", () => {
  const cb = jest.fn();
  setTimeout(cb, 1000);
  jest.advanceTimersByTime(1000);
  expect(cb).toHaveBeenCalled();
});

Test Terparameterisasi

test.each([
  [1, 1, 2],
  [2, 3, 5],
])("add(%i, %i) = %i", (a, b, expected) => {
  expect(add(a, b)).toBe(expected);
});

Custom Matcher

expect.extend({
  toBeWithinRange(received, floor, ceil) {
    const pass = received >= floor
      && received <= ceil;
    return { pass, message: () =>
      `expected ${received} in [${floor},${ceil}]` };
}});

REFERENSI CEPAT JEST