Python 测试模式
使用 pytest、TDD 方法论和最佳实践的 Python 应用程序全面测试策略。
何时激活
- 编写新的 Python 代码（遵循 TDD：红、绿、重构）
- 为 Python 项目设计测试套件
- 审查 Python 测试覆盖率
- 设置测试基础设施
核心测试理念
测试驱动开发 (TDD)
始终遵循 TDD 循环：
- 红：为期望的行为编写一个失败的测试
- 绿：编写最少的代码使测试通过
- 重构：在保持测试通过的同时改进代码
python
# Step 1: Write failing test (RED)def test_add_numbers(): result = add(2, 3) assert result == 5
# Step 2: Write minimal implementation (GREEN)def add(a, b): return a + b
# Step 3: Refactor if needed (REFACTOR)覆盖率要求
- 目标：80%+ 代码覆盖率
- 关键路径：需要 100% 覆盖率
- 使用
pytest --cov来测量覆盖率
bash
pytest --cov=mypackage --cov-report=term-missing --cov-report=htmlpytest 基础
基本测试结构
python
import pytest
def test_addition(): """Test basic addition.""" assert 2 + 2 == 4
def test_string_uppercase(): """Test string uppercasing.""" text = "hello" assert text.upper() == "HELLO"
def test_list_append(): """Test list append.""" items = [1, 2, 3] items.append(4) assert 4 in items assert len(items) == 4断言
python
# Equalityassert result == expected
# Inequalityassert result != unexpected
# Truthinessassert result # Truthyassert not result # Falsyassert result is True # Exactly Trueassert result is False # Exactly Falseassert result is None # Exactly None
# Membershipassert item in collectionassert item not in collection
# Comparisonsassert result > 0assert 0 <= result <= 100
# Type checkingassert isinstance(result, str)
# Exception testing (preferred approach)with pytest.raises(ValueError): raise ValueError("error message")
# Check exception messagewith pytest.raises(ValueError, match="invalid input"): raise ValueError("invalid input provided")
# Check exception attributeswith pytest.raises(ValueError) as exc_info: raise ValueError("error message")assert str(exc_info.value) == "error message"夹具
基本夹具使用
python
import pytest
@pytest.fixturedef sample_data(): """Fixture providing sample data.""" return {"name": "Alice", "age": 30}
def test_sample_data(sample_data): """Test using the fixture.""" assert sample_data["name"] == "Alice" assert sample_data["age"] == 30带设置/拆卸的夹具
python
@pytest.fixturedef database(): """Fixture with setup and teardown.""" # Setup db = Database(":memory:") db.create_tables() db.insert_test_data()
yield db # Provide to test
# Teardown db.close()
def test_database_query(database): """Test database operations.""" result = database.query("SELECT * FROM users") assert len(result) > 0夹具作用域
python
# Function scope (default) - runs for each test@pytest.fixturedef temp_file(): with open("temp.txt", "w") as f: yield f os.remove("temp.txt")
# Module scope - runs once per module@pytest.fixture(scope="module")def module_db(): db = Database(":memory:") db.create_tables() yield db db.close()
# Session scope - runs once per test session@pytest.fixture(scope="session")def shared_resource(): resource = ExpensiveResource() yield resource resource.cleanup()带参数的夹具
python
@pytest.fixture(params=[1, 2, 3])def number(request): """Parameterized fixture.""" return request.param
def test_numbers(number): """Test runs 3 times, once for each parameter.""" assert number > 0使用多个夹具
python
@pytest.fixturedef user(): return User(id=1, name="Alice")
@pytest.fixturedef admin(): return User(id=2, name="Admin", role="admin")
def test_user_admin_interaction(user, admin): """Test using multiple fixtures.""" assert admin.can_manage(user)自动使用夹具
python
@pytest.fixture(autouse=True)def reset_config(): """Automatically runs before every test.""" Config.reset() yield Config.cleanup()
def test_without_fixture_call(): # reset_config runs automatically assert Config.get_setting("debug") is False使用 Conftest.py 共享夹具
python
# tests/conftest.pyimport pytest
@pytest.fixturedef client(): """Shared fixture for all tests.""" app = create_app(testing=True) with app.test_client() as client: yield client
@pytest.fixturedef auth_headers(client): """Generate auth headers for API testing.""" response = client.post("/api/login", json={ "username": "test", "password": "test" }) token = response.json["token"] return {"Authorization": f"Bearer {token}"}参数化
基本参数化
python
@pytest.mark.parametrize("input,expected", [ ("hello", "HELLO"), ("world", "WORLD"), ("PyThOn", "PYTHON"),])def test_uppercase(input, expected): """Test runs 3 times with different inputs.""" assert input.upper() == expected多参数
python
@pytest.mark.parametrize("a,b,expected", [ (2, 3, 5), (0, 0, 0), (-1, 1, 0), (100, 200, 300),])def test_add(a, b, expected): """Test addition with multiple inputs.""" assert add(a, b) == expected带 ID 的参数化
python
@pytest.mark.parametrize("input,expected", [ ("[email protected]", True), ("invalid", False), ("@no-domain.com", False),], ids=["valid-email", "missing-at", "missing-domain"])def test_email_validation(input, expected): """Test email validation with readable test IDs.""" assert is_valid_email(input) is expected参数化夹具
python
@pytest.fixture(params=["sqlite", "postgresql", "mysql"])def db(request): """Test against multiple database backends.""" if request.param == "sqlite": return Database(":memory:") elif request.param == "postgresql": return Database("postgresql://localhost/test") elif request.param == "mysql": return Database("mysql://localhost/test")
def test_database_operations(db): """Test runs 3 times, once for each database.""" result = db.query("SELECT 1") assert result is not None标记器和测试选择
自定义标记器
python
# Mark slow tests@pytest.mark.slowdef test_slow_operation(): time.sleep(5)
# Mark integration tests@pytest.mark.integrationdef test_api_integration(): response = requests.get("https://api.example.com") assert response.status_code == 200
# Mark unit tests@pytest.mark.unitdef test_unit_logic(): assert calculate(2, 3) == 5运行特定测试
bash
# Run only fast testspytest -m "not slow"
# Run only integration testspytest -m integration
# Run integration or slow testspytest -m "integration or slow"
# Run tests marked as unit but not slowpytest -m "unit and not slow"在 pytest.ini 中配置标记器
ini
[pytest]markers = slow: marks tests as slow integration: marks tests as integration tests unit: marks tests as unit tests django: marks tests as requiring Django模拟和补丁
模拟函数
python
from unittest.mock import patch, Mock
@patch("mypackage.external_api_call")def test_with_mock(api_call_mock): """Test with mocked external API.""" api_call_mock.return_value = {"status": "success"}
result = my_function()
api_call_mock.assert_called_once() assert result["status"] == "success"模拟返回值
python
@patch("mypackage.Database.connect")def test_database_connection(connect_mock): """Test with mocked database connection.""" connect_mock.return_value = MockConnection()
db = Database() db.connect()
connect_mock.assert_called_once_with("localhost")模拟异常
python
@patch("mypackage.api_call")def test_api_error_handling(api_call_mock): """Test error handling with mocked exception.""" api_call_mock.side_effect = ConnectionError("Network error")
with pytest.raises(ConnectionError): api_call()
api_call_mock.assert_called_once()模拟上下文管理器
python
@patch("builtins.open", new_callable=mock_open)def test_file_reading(mock_file): """Test file reading with mocked open.""" mock_file.return_value.read.return_value = "file content"
result = read_file("test.txt")
mock_file.assert_called_once_with("test.txt", "r") assert result == "file content"使用 Autospec
python
@patch("mypackage.DBConnection", autospec=True)def test_autospec(db_mock): """Test with autospec to catch API misuse.""" db = db_mock.return_value db.query("SELECT * FROM users")
# This would fail if DBConnection doesn't have query method db_mock.assert_called_once()模拟类实例
python
class TestUserService: @patch("mypackage.UserRepository") def test_create_user(self, repo_mock): """Test user creation with mocked repository.""" repo_mock.return_value.save.return_value = User(id=1, name="Alice")
service = UserService(repo_mock.return_value) user = service.create_user(name="Alice")
assert user.name == "Alice" repo_mock.return_value.save.assert_called_once()模拟属性
python
@pytest.fixturedef mock_config(): """Create a mock with a property.""" config = Mock() type(config).debug = PropertyMock(return_value=True) type(config).api_key = PropertyMock(return_value="test-key") return config
def test_with_mock_config(mock_config): """Test with mocked config properties.""" assert mock_config.debug is True assert mock_config.api_key == "test-key"测试异步代码
使用 pytest-asyncio 进行异步测试
python
import pytest
@pytest.mark.asyncioasync def test_async_function(): """Test async function.""" result = await async_add(2, 3) assert result == 5
@pytest.mark.asyncioasync def test_async_with_fixture(async_client): """Test async with async fixture.""" response = await async_client.get("/api/users") assert response.status_code == 200异步夹具
python
@pytest.fixtureasync def async_client(): """Async fixture providing async test client.""" app = create_app() async with app.test_client() as client: yield client
@pytest.mark.asyncioasync def test_api_endpoint(async_client): """Test using async fixture.""" response = await async_client.get("/api/data") assert response.status_code == 200模拟异步函数
python
@pytest.mark.asyncio@patch("mypackage.async_api_call")async def test_async_mock(api_call_mock): """Test async function with mock.""" api_call_mock.return_value = {"status": "ok"}
result = await my_async_function()
api_call_mock.assert_awaited_once() assert result["status"] == "ok"测试异常
测试预期异常
python
def test_divide_by_zero(): """Test that dividing by zero raises ZeroDivisionError.""" with pytest.raises(ZeroDivisionError): divide(10, 0)
def test_custom_exception(): """Test custom exception with message.""" with pytest.raises(ValueError, match="invalid input"): validate_input("invalid")测试异常属性
python
def test_exception_with_details(): """Test exception with custom attributes.""" with pytest.raises(CustomError) as exc_info: raise CustomError("error", code=400)
assert exc_info.value.code == 400 assert "error" in str(exc_info.value)测试副作用
测试文件操作
python
import tempfileimport os
def test_file_processing(): """Test file processing with temp file.""" with tempfile.NamedTemporaryFile(mode='w', delete=False, suffix='.txt') as f: f.write("test content") temp_path = f.name
try: result = process_file(temp_path) assert result == "processed: test content" finally: os.unlink(temp_path)使用 pytest 的 tmp_path 夹具进行测试
python
def test_with_tmp_path(tmp_path): """Test using pytest's built-in temp path fixture.""" test_file = tmp_path / "test.txt" test_file.write_text("hello world")
result = process_file(str(test_file)) assert result == "hello world" # tmp_path automatically cleaned up使用 tmpdir 夹具进行测试
python
def test_with_tmpdir(tmpdir): """Test using pytest's tmpdir fixture.""" test_file = tmpdir.join("test.txt") test_file.write("data")
result = process_file(str(test_file)) assert result == "data"测试组织
目录结构
tests/├── conftest.py # 共享 fixtures├── __init__.py├── unit/ # 单元测试│ ├── __init__.py│ ├── test_models.py│ ├── test_utils.py│ └── test_services.py├── integration/ # 集成测试│ ├── __init__.py│ ├── test_api.py│ └── test_database.py└── e2e/ # 端到端测试 ├── __init__.py └── test_user_flow.py测试类
python
class TestUserService: """Group related tests in a class."""
@pytest.fixture(autouse=True) def setup(self): """Setup runs before each test in this class.""" self.service = UserService()
def test_create_user(self): """Test user creation.""" user = self.service.create_user("Alice") assert user.name == "Alice"
def test_delete_user(self): """Test user deletion.""" user = User(id=1, name="Bob") self.service.delete_user(user) assert not self.service.user_exists(1)最佳实践
应该做
- 遵循 TDD：在代码之前编写测试（红-绿-重构）
- 测试单一事物：每个测试应验证一个单一行为
- 使用描述性名称：
test_user_login_with_invalid_credentials_fails - 使用夹具：用夹具消除重复
- 模拟外部依赖：不要依赖外部服务
- 测试边界情况：空输入、None 值、边界条件
- 目标 80%+ 覆盖率：关注关键路径
- 保持测试快速：使用标记来分离慢速测试
不要做
- 不要测试实现：测试行为，而非内部实现
- 不要在测试中使用复杂的条件语句：保持测试简单
- 不要忽略测试失败：所有测试必须通过
- 不要测试第三方代码：相信库能正常工作
- 不要在测试之间共享状态：测试应该是独立的
- 不要在测试中捕获异常：使用
pytest.raises - 不要使用 print 语句：使用断言和 pytest 输出
- 不要编写过于脆弱的测试：避免过度具体的模拟
常见模式
测试 API 端点 (FastAPI/Flask)
python
@pytest.fixturedef client(): app = create_app(testing=True) return app.test_client()
def test_get_user(client): response = client.get("/api/users/1") assert response.status_code == 200 assert response.json["id"] == 1
def test_create_user(client): response = client.post("/api/users", json={ "name": "Alice", "email": "[email protected]" }) assert response.status_code == 201 assert response.json["name"] == "Alice"测试数据库操作
python
@pytest.fixturedef db_session(): """Create a test database session.""" session = Session(bind=engine) session.begin_nested() yield session session.rollback() session.close()
def test_create_user(db_session): user = User(name="Alice", email="[email protected]") db_session.add(user) db_session.commit()
retrieved = db_session.query(User).filter_by(name="Alice").first() assert retrieved.email == "[email protected]"测试类方法
python
class TestCalculator: @pytest.fixture def calculator(self): return Calculator()
def test_add(self, calculator): assert calculator.add(2, 3) == 5
def test_divide_by_zero(self, calculator): with pytest.raises(ZeroDivisionError): calculator.divide(10, 0)pytest 配置
pytest.ini
ini
[pytest]testpaths = testspython_files = test_*.pypython_classes = Test*python_functions = test_*addopts = --strict-markers --disable-warnings --cov=mypackage --cov-report=term-missing --cov-report=htmlmarkers = slow: marks tests as slow integration: marks tests as integration tests unit: marks tests as unit testspyproject.toml
toml
[tool.pytest.ini_options]testpaths = ["tests"]python_files = ["test_*.py"]python_classes = ["Test*"]python_functions = ["test_*"]addopts = [ "--strict-markers", "--cov=mypackage", "--cov-report=term-missing", "--cov-report=html",]markers = [ "slow: marks tests as slow", "integration: marks tests as integration tests", "unit: marks tests as unit tests",]运行测试
bash
# Run all testspytest
# Run specific filepytest tests/test_utils.py
# Run specific testpytest tests/test_utils.py::test_function
# Run with verbose outputpytest -v
# Run with coveragepytest --cov=mypackage --cov-report=html
# Run only fast testspytest -m "not slow"
# Run until first failurepytest -x
# Run and stop on N failurespytest --maxfail=3
# Run last failed testspytest --lf
# Run tests with patternpytest -k "test_user"
# Run with debugger on failurepytest --pdb快速参考
| 模式 | 用法 |
|---|---|
pytest.raises() | 测试预期异常 |
@pytest.fixture() | 创建可重用的测试夹具 |
@pytest.mark.parametrize() | 使用多个输入运行测试 |
@pytest.mark.slow | 标记慢速测试 |
pytest -m "not slow" | 跳过慢速测试 |
@patch() | 模拟函数和类 |
tmp_path 夹具 | 自动临时目录 |
pytest --cov | 生成覆盖率报告 |
assert | 简单且可读的断言 |
记住：测试也是代码。保持它们干净、可读且可维护。好的测试能发现错误；优秀的测试能预防错误。
