Fixture 指南

基础 Fixture 与作用域

import pytest

# function 作用域（默认）— 每个测试创建新实例
@pytest.fixture
def db_connection():
    conn = create_connection("sqlite:///:memory:")
    yield conn
    conn.close()

# module 作用域 — 同文件内共享
@pytest.fixture(scope="module")
def http_client():
    return TestClient(app)

# session 作用域 — 整个测试会话共享
@pytest.fixture(scope="session")
def app_config():
    return load_config("test.yaml")

# 作用域优先级（从宽到窄）：
# session > package > module > class > function

conftest.py — 共享 Fixtures

# conftest.py（放在项目根目录或测试目录）
import pytest
from myapp import create_app, db as _db

@pytest.fixture(scope="session")
def app():
    app = create_app({"TESTING": True, "DATABASE_URL": "sqlite:///:memory:"})
    return app

@pytest.fixture(scope="session")
def db(app):
    with app.app_context():
        _db.create_all()
        yield _db
        _db.drop_all()

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

@pytest.fixture
def auth_headers():
    token = generate_test_token(user_id=1, role="admin")
    return {"Authorization": f"Bearer {token}"}

# conftest.py 被 pytest 自动发现，无需在测试文件中导入

yield Fixtures — 初始化与清理

import pytest from unittest.mock import patch @pytest.fixture def mock_external_api(): with patch("myapp.services.requests.get") as mock_get: mock_get.return_value.json.return_value = {"status": "ok"} mock_get.return_value.status_code = 200 yield mock_get # yield 之后的代码自动作为清理逻辑执行 @pytest.fixture def temp_user(db): user = User(name="测试用户", email="[email protected]") db.session.add(user) db.session.commit() yield user db.session.delete(user) db.session.commit()

参数化 Fixtures

import pytest

@pytest.fixture(params=["sqlite", "postgres", "mysql"])
def database(request):
    """针对多个数据库后端运行测试。"""
    db_type = request.param
    conn = connect_to_db(db_type)
    yield conn
    conn.close()

def test_insert_record(database):
    # 该测试运行 3 次，每种数据库各一次
    database.execute("INSERT INTO users (name) VALUES ('张三')")
    result = database.execute("SELECT * FROM users").fetchall()
    assert len(result) == 1

autouse Fixtures

import pytest

# 自动应用于作用域内所有测试
@pytest.fixture(autouse=True)
def reset_database(db):
    yield
    db.session.rollback()

# 类级别 autouse
class TestPayments:
    @pytest.fixture(autouse=True)
    def setup_payment_gateway(self):
        with patch("myapp.payments.stripe") as mock_stripe:
            mock_stripe.charge.return_value = {"id": "ch_test"}
            self.stripe = mock_stripe
            yield

tmpdir / tmp_path — 临时文件

import pytest

# tmp_path（现代写法，pathlib.Path，推荐）
def test_writes_output_file(tmp_path):
    output_file = tmp_path / "output.txt"
    write_report(output_file)
    assert output_file.exists()
    assert output_file.read_text() == "报告完成\n"

# tmp_path_factory 用于 session 作用域临时目录
@pytest.fixture(scope="session")
def shared_data_dir(tmp_path_factory):
    base = tmp_path_factory.mktemp("data")
    (base / "sample.csv").write_text("id,name\n1,张三\n")
    return base