如何在FastAPI Strawberry中使用独立测试数据库测试GraphQL端点？

1. 使用Alembic为测试数据库执行迁移 #

Alembic支持通过配置切换目标数据库，你可以通过以下方式实现测试库的迁移：

方式一：通过命令行参数指定测试库URL #

在测试前调用Alembic命令，传入测试数据库的URL：

import pytest
from alembic.config import Config
from alembic import command

@pytest.fixture(scope="session")
def test_db_migrations():
    # 加载Alembic配置
    alembic_cfg = Config("alembic.ini")
    # 替换配置中的数据库URL为测试库地址
    alembic_cfg.set_main_option(
        "sqlalchemy.url", 
        "postgresql://user:password@localhost/test_db"
    )
    # 执行迁移到最新版本
    command.upgrade(alembic_cfg, "head")
    yield
    # 测试完成后回滚到初始状态（可选）
    command.downgrade(alembic_cfg, "base")

方式二：用子进程执行迁移命令 #

如果更习惯命令行操作，也可以直接调用subprocess：

import subprocess
import pytest

@pytest.fixture(scope="session")
def test_db_migrations():
    subprocess.run(
        ["alembic", "upgrade", "head", "-x", "db_url=postgresql://user:password@localhost/test_db"],
        check=True
    )
    yield
    subprocess.run(
        ["alembic", "downgrade", "base", "-x", "db_url=postgresql://user:password@localhost/test_db"],
        check=True
    )

2. 替换Strawberry字段中的数据库会话 #

Strawberry支持依赖注入，和FastAPI的逻辑一致，你可以通过依赖重载实现测试会话替换：

第一步：封装数据库会话依赖 #

先把主库和测试库的会话封装成可替换的依赖：

# db/deps.py
from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker, Session

# 主库配置
MAIN_DB_URL = "postgresql://user:password@localhost/main_db"
# 测试库配置
TEST_DB_URL = "postgresql://user:password@localhost/test_db"

def get_main_db_session() -> Session:
    engine = create_engine(MAIN_DB_URL)
    SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)
    db = SessionLocal()
    try:
        yield db
    finally:
        db.close()

def get_test_db_session() -> Session:
    engine = create_engine(TEST_DB_URL)
    SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)
    db = SessionLocal()
    try:
        yield db
    finally:
        db.close()

第二步：在Strawberry Resolver中注入依赖 #

在字段定义时通过strawberry.dependency引入会话：

import strawberry
from sqlalchemy.orm import Session
from db.deps import get_main_db_session
from models import User

@strawberry.type
class Query:
    @strawberry.field
    def get_user(self, id: int, db: Session = strawberry.dependency(get_main_db_session)) -> User:
        return db.query(User).filter(User.id == id).first()

第三步：测试时重载依赖 #

在pytest fixture中替换Strawberry的依赖：

# conftest.py
import pytest
from strawberry.fastapi import GraphQLRouter
from fastapi.testclient import TestClient
from main import app, graphql_app
from db.deps import get_main_db_session, get_test_db_session

@pytest.fixture(scope="function")
def client():
    # 重载依赖，用测试库会话替换主库会话
    graphql_app.override_dependency(get_main_db_session, get_test_db_session)
    client = TestClient(app)
    yield client
    # 测试完成后恢复原依赖
    graphql_app.reset_overrides()

3. 使用Requests模块测试GraphQL端点 #

直接构造GraphQL请求的JSON数据，发送到端点即可：

def test_get_user(client):
    # 定义GraphQL查询
    query = """
    query GetUser($id: Int!) {
        getUser(id: $id) {
            id
            name
            email
        }
    }
    """
    # 发送POST请求
    response = client.post(
        "/graphql",
        json={
            "query": query,
            "variables": {"id": 1}
        }
    )
    # 断言结果
    assert response.status_code == 200
    data = response.json()
    assert "errors" not in data
    assert data["data"]["getUser"]["id"] == 1

如果不用FastAPI的TestClient，直接用原生requests库：

import requests

def test_get_user():
    query = """
    query GetUser($id: Int!) {
        getUser(id: $id) {
            id
            name
        }
    }
    """
    response = requests.post(
        "http://localhost:8000/graphql",
        json={
            "query": query,
            "variables": {"id": 1}
        }
    )
    assert response.status_code == 200
    assert "errors" not in response.json()

内容的提问来源于stack exchange，提问作者iljuhenson