Mocks, stubs, da test doubles me nawa?

Question

Accepted Answer

**Test doubles** su ne abubuwa da suke tsaye don ainihi na dogaro a cikin gwaje — hardai da **mocks**, **stubs**, **spies**, **fakes**, da **dummies**. Suna kewarewa koda da ake gwada daga doganonsa (databases, APIs, services), wanda ke haifar da gwaje masu sauri, masu maido, da na iko.

## Dalilin 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)
```

## Nau'ikan 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 da stub (bambance-bambancen mahimma)

```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.
```

## Me ya sa haka ya zama mahimma

Ganewa test doubles (mocks, stubs, da sauransu) yana da mahimmanci saboda suna **da mahimmanci wajen rubuta gwaje masu kewarewa koda**, don haka gida ne, sannu-sannu an amfani da ilimin gwaje.

Don gwada koda a kewarera (gida na gwaje na koda), dole ne ka maye koda na dogaro na ainihi (databases, APIs, services) da **test doubles** — wanda ke haifar da gwaje da suke **sauri** (babu ainihi na I/O), **iko** (saitawa wurare na adadi da kuma huje wanda ba zai yiwu yin akawa dogaro na ainihi ba), da **a gefen wannan** (babu waje na rashin kwanciyar hankali).

Ganewa **nau'ikan** da wuraren aiki su yana bukatar: **stubs** (abubuwan da ke ba da amsa da aka shimma don sarrafa abin da dogaro ke bada — abubuwan da ke jefar da koda musamman bayani), **mocks** (stubs da kuma sune gane dawayi — duba koda ta kira dogaro cikin daidai), **spies** (rubuta kira a ainihi ko karya abubuwa), **fakes** (aiki na saukar-saukar kasusuwa kamar ƙwarewar memory), da **dummies** (wuri makale).

Ganewa **bambance-bambancen mahimma mock da stub** — stubs sune sarrafa abubuwan shiga (nuni gida: ba da bayani) yayin da mocks sune gane abubuwan fitarwa/dawayi (nuni hali: duba koda ta kira dogaro cikin daidai) — yana da mahimmanci gida ilimin sauran lokaci an rudu, da amfani kowannen a daidai zai aiki.

Ganewa **matsalar over-mocking** (mocking ba sai yana rabo gwaje don abubuwan aiki, wanda ke haifar da rashin karfi, don haka ka ya kamata mocking a matsayar daidai) tana nuni ta bukataccen ilimin gwaje.

Test doubles ana amfani su a koyaushe a gwaje na koda don kewarewa koda da ake gwada.

Saboda kewarewa koda dole ne za a maye ainihi dogaro da test doubles (don sauri, iko, da adadi), da saboda ganewa nau'ikan, bambance-bambancen mock da stub, da matsalar over-mocking yana bukatar don rubuta gwaje mabura kewarewa, ganewa test doubles yana da mahimmanci, sannu-sannu an amfani da ilimin gwaje — da mahimmanci wajen gwaje na koda, ana amfani da shi a koyaushe don kewarewa koda, da mahimmanci wajen rubuta gwaje masu maido, kewarewa wada ba amfani da over-mocking, fa shawara ta mahimmanci wajen bukataccen gwaje na koda.