Apa iku mocks, stubs, lan test doubles?

Question

Accepted Answer

**Test doubles** yaiku obyek sing dadi gantine dependensi nyata ing tes — kalebu **mocks**, **stubs**, **spies**, **fakes**, lan **dummies**. Kaakeh pisahin kode sing diuji saka dependensine (database, API, layanan), ngawonake tes unit sing cepet, fokus, lan terkontrol.

## Mengapa test doubles

```text
To test a unit in ISOLATION, replace its real dependencies (DB, API, services) with
TEST DOUBLES (fake stand-ins):
  → isolate the unit (test ONLY it, not its dependencies)
  → FAST (no real DB/network); CONTROLLED (set up exact scenarios, including errors);
    DETERMINISTIC (no external flakiness)
```

## Jenis-jenis test doubles

```text
STUB → provides canned RESPONSES to calls (returns preset data):
  → "when getUser is called, return this fake user" — controls inputs to the unit
MOCK → a stub that also VERIFIES interactions (was it called? how? with what?):
  → "verify save() was called once with these arguments" — checks behavior/interactions
SPY → wraps a real (or fake) object and RECORDS calls (verify how it was used)
FAKE → a working but simplified implementation (e.g. an in-memory database)
DUMMY → a placeholder passed but not actually used
```

```js
// stub: control what a dependency returns
const userService = { getUser: jest.fn().mockReturnValue({ name: 'Ann' }) };
// mock verification: check an interaction happened
expect(emailService.send).toHaveBeenCalledWith('ann@x.com');
```

## Mock vs stub (pembedane penting)

```text
STUB → controls INPUTS (provides data the unit needs) — "state" verification
MOCK → verifies OUTPUTS/interactions (was the dependency called correctly?) — "behavior"
  verification
→ Use stubs to provide data; mocks to verify the unit called a dependency correctly.
⚠️ Over-mocking → tests coupled to implementation (brittle); mock at the right boundaries.
```

## Mengapa iku penting

Ngerteni test doubles (mocks, stubs, lsp.) iku penting amarga kaakeh **kudu ana kanggo nulis tes unit sing terisolasi**, mula iku pengetahuan testing sing berharga lan kerap digunakake.

Kanggo ngetest unit kanthi terisolasi (tujuan unit testing), sampeyan kudu ngganti dependensi nyatane (database, API, layanan) karo **test doubles** — ngawonake tes sing **cepet** (tanpa I/O nyata), **terkontrol** (nyetel skenario persis kalebu kondisi kesalahan sing angel dipicu nganggo dependensi nyata), lan **deterministic** (tanpa keragaman eksternal).

Ngerteni **jenis-jenise** lan tujuane mula kudu: **stubs** (nyediakake canned responses kanggo ngontrol apa sing balik dependensi — nyedhiakake data spesifik kanggo unit), **mocks** (stubs sing uga verify interaksi — mriksa unit ngajak dependensi kanthi bener), **spies** (ngrékam panggilan ing obyek nyata utawa palsu), **fakes** (implementasi sederhana sing bisa digunakake liyane kayata database in-memory), lan **dummies** (placeholders).

Ngerteni **pembedane penting mock-vs-stub** — stubs ngontrol input (state verification: nyediakake data) dene mocks verify output/interaksi (behavior verification: mriksa unit ngajak dependensi kanthi bener) — iku pengetahuan konseptual penting sing kerap bingung, lan nggunakake masing-masing kanthi layak iku penting.

Ngerteni **jebakan over-mocking** (mocking kalebihan nggandhul tes ing detail implementasi, ndadekake kasar, mula sampeyan kudhu mock ing batas sing tepat) nunjukake pertimbangan testing sing dewasa.

Test doubles digunakake terus-terusan ing unit testing kanggo pisahin kode sing diuji.

Kareben terisolasi unit testing butuh ngganti dependensi nyata karo test doubles (kanggo kecepatan, kontrol, lan determinisme), lan sebab ngerteni jenis-jenise, pembedane mock-vs-stub, lan jebakan over-mocking iku kudu kanggo nulis tes terisolasi sing apik, ngerteni test doubles yaiku pengetahuan testing sing berharga lan kerap digunakake — kudu ana kanggo unit testing, digunakake terus-terusan kanggo pisahin kode, lan penting kanggo nulis tes fokus, terkontrol sambil ngindhari kageripan over-mocking, skill inti kanggo unit testing sing efektif.