# Referensi Cepat Jest

*Test, matcher, mocking, async, dan snapshot*

> Source: Jest Documentation (jestjs.io) · MIT

## 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

| Command | Description |
|---------|-------------|
| `*.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

| Command | Description |
|---------|-------------|
| `test.skip()` | Lewati test ini |
| `test.only()` | Jalankan hanya test ini |
| `describe.skip()` | Lewati seluruh suite |
| `describe.only()` | Jalankan hanya suite ini |

## Matcher

### Kesamaan

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

### Truthiness

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

### Angka

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

### String, Array, Objek

| Command | Description |
|---------|-------------|
| `.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

| Command | Description |
|---------|-------------|
| `.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(<App />).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

| Command | Description |
|---------|-------------|
| `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}]` };
}});
```