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FastAPI 테스팅

FastAPI는 TestClient (동기)와 AsyncClient (비동기)로 API를 테스트합니다.

TestClient 기초​

# pip install httpx

from fastapi import FastAPI
from fastapi.testclient import TestClient
import pytest

app = FastAPI()

fake_db: dict[int, dict] = {}
next_id = 1


@app.post("/users/", status_code=201)
def create_user(name: str, email: str):
    global next_id
    user = {"id": next_id, "name": name, "email": email}
    fake_db[next_id] = user
    next_id += 1
    return user


@app.get("/users/{user_id}")
def get_user(user_id: int):
    from fastapi import HTTPException
    if user_id not in fake_db:
        raise HTTPException(status_code=404, detail="User not found")
    return fake_db[user_id]


# 테스트
client = TestClient(app)


def test_create_user():
    response = client.post("/users/?name=Alice&email=alice@example.com")
    assert response.status_code == 201
    data = response.json()
    assert data["name"] == "Alice"
    assert "id" in data


def test_get_user():
    # 먼저 생성
    create_resp = client.post("/users/?name=Bob&email=bob@test.com")
    user_id = create_resp.json()["id"]

    # 조회
    response = client.get(f"/users/{user_id}")
    assert response.status_code == 200
    assert response.json()["name"] == "Bob"


def test_user_not_found():
    response = client.get("/users/9999")
    assert response.status_code == 404
    assert "not found" in response.json()["detail"].lower()

pytest fixture와 DB 격리​

import pytest
from fastapi.testclient import TestClient
from sqlalchemy import create_engine, StaticPool
from sqlalchemy.orm import sessionmaker
from database import Base, get_db, User
from main import app

# 테스트용 메모리 DB
TEST_DATABASE_URL = "sqlite:///:memory:"

test_engine = create_engine(
    TEST_DATABASE_URL,
    connect_args={"check_same_thread": False},
    poolclass=StaticPool,
)
TestingSessionLocal = sessionmaker(bind=test_engine)


@pytest.fixture(autouse=True)
def setup_db():
    """각 테스트마다 새 테이블 생성·삭제"""
    Base.metadata.create_all(bind=test_engine)
    yield
    Base.metadata.drop_all(bind=test_engine)


@pytest.fixture
def db_session():
    session = TestingSessionLocal()
    try:
        yield session
    finally:
        session.close()


@pytest.fixture
def client(db_session):
    """DB 의존성을 테스트 DB로 교체"""
    def override_get_db():
        yield db_session

    app.dependency_overrides[get_db] = override_get_db
    with TestClient(app) as test_client:
        yield test_client
    app.dependency_overrides.clear()


def test_create_user(client):
    response = client.post(
        "/users/",
        json={"name": "Alice", "email": "alice@example.com", "password": "secret"},
    )
    assert response.status_code == 201
    assert response.json()["email"] == "alice@example.com"


def test_duplicate_email(client):
    data = {"name": "Alice", "email": "dup@test.com", "password": "pass"}
    client.post("/users/", json=data)

    response = client.post("/users/", json=data)
    assert response.status_code == 400

인증 테스트​

import pytest
from fastapi.testclient import TestClient
from main import app


@pytest.fixture
def client():
    return TestClient(app)


@pytest.fixture
def auth_headers(client):
    """로그인 후 헤더 반환"""
    response = client.post(
        "/auth/login",
        data={"username": "alice", "password": "password123"},
    )
    token = response.json()["access_token"]
    return {"Authorization": f"Bearer {token}"}


def test_login_success(client):
    response = client.post(
        "/auth/login",
        data={"username": "alice", "password": "password123"},
    )
    assert response.status_code == 200
    assert "access_token" in response.json()


def test_login_wrong_password(client):
    response = client.post(
        "/auth/login",
        data={"username": "alice", "password": "wrong"},
    )
    assert response.status_code == 401


def test_protected_endpoint_without_token(client):
    response = client.get("/users/me")
    assert response.status_code == 401


def test_protected_endpoint_with_token(client, auth_headers):
    response = client.get("/users/me", headers=auth_headers)
    assert response.status_code == 200
    assert response.json()["username"] == "alice"


def test_admin_only_endpoint(client, auth_headers):
    """alice는 admin 역할"""
    response = client.get("/admin/users", headers=auth_headers)
    assert response.status_code == 200

pytest-asyncio — 비동기 테스트​

# pip install pytest-asyncio httpx

import pytest
import pytest_asyncio
from httpx import AsyncClient, ASGITransport
from main import app


@pytest.mark.asyncio
async def test_async_endpoint():
    async with AsyncClient(
        transport=ASGITransport(app=app),
        base_url="http://test"
    ) as client:
        response = await client.get("/")
        assert response.status_code == 200


# 비동기 fixture
@pytest_asyncio.fixture
async def async_client():
    async with AsyncClient(
        transport=ASGITransport(app=app),
        base_url="http://test"
    ) as client:
        yield client


@pytest.mark.asyncio
async def test_create_item(async_client):
    response = await async_client.post(
        "/items/",
        json={"name": "Test Item", "price": 10.5},
    )
    assert response.status_code == 201
    assert response.json()["name"] == "Test Item"


@pytest.mark.asyncio
async def test_concurrent_requests(async_client):
    import asyncio
    responses = await asyncio.gather(*[
        async_client.get(f"/items/{i}")
        for i in range(10)
    ])
    assert all(r.status_code in (200, 404) for r in responses)

정리​

도구용도
TestClient동기 테스트 (대부분의 경우)
AsyncClient비동기 엔드포인트 테스트
dependency_overridesDB 등 의존성 교체
pytest.fixture클라이언트, DB 세션 공유
pytest-asyncioasync 테스트 함수 지원

FastAPI 테스트는 실제 HTTP 요청 흐름(미들웨어 포함)을 검증하는 통합 테스트 방식으로 작성하세요.

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