pytest、TDD手法、フィクスチャ、モック、パラメータ化、カバレッジ要件を使用したPythonテスト戦略。
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---
name: python-testing
description: pytest、TDD手法、フィクスチャ、モック、パラメータ化、カバレッジ要件を使用したPythonテスト戦略。
source_path: skills/python-testing/SKILL.md
---
# Pythonテストパターン
pytest、TDD方法論、ベストプラクティスを使用したPythonアプリケーションの包括的なテスト戦略。
## いつ有効化するか
- 新しいPythonコードを書くとき（TDDに従う：赤、緑、リファクタリング）
- Pythonプロジェクトのテストスイートを設計するとき
- Pythonテストカバレッジをレビューするとき
- テストインフラストラクチャをセットアップするとき
## 核となるテスト哲学
### テスト駆動開発（TDD）
常にTDDサイクルに従います。
1. **赤**: 期待される動作のための失敗するテストを書く
2. **緑**: テストを通過させるための最小限のコードを書く
3. **リファクタリング**: テストを通過させたままコードを改善する
```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)
```
### カバレッジ要件
- **目標**: 80%以上のコードカバレッジ
- **クリティカルパス**: 100%のカバレッジが必要
- `pytest --cov`を使用してカバレッジを測定
```bash
pytest --cov=mypackage --cov-report=term-missing --cov-report=html
```
## pytestの基礎
### 基本的なテスト構造
```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
```
### アサーション
```python
# Equality
assert result == expected
# Inequality
assert result != unexpected
# Truthiness
assert result # Truthy
assert not result # Falsy
assert result is True # Exactly True
assert result is False # Exactly False
assert result is None # Exactly None
# Membership
assert item in collection
assert item not in collection
# Comparisons
assert result > 0
assert 0 <= result <= 100
# Type checking
assert isinstance(result, str)
# Exception testing (preferred approach)
with pytest.raises(ValueError):
raise ValueError("error message")
# Check exception message
with pytest.raises(ValueError, match="invalid input"):
raise ValueError("invalid input provided")
# Check exception attributes
with pytest.raises(ValueError) as exc_info:
raise ValueError("error message")
assert str(exc_info.value) == "error message"
```
## フィクスチャ
### 基本的なフィクスチャ使用
```python
import pytest
@pytest.fixture
def 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
```
### セットアップ/ティアダウン付きフィクスチャ
```python
@pytest.fixture
def 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
```
### フィクスチャスコープ
```python
# Function scope (default) - runs for each test
@pytest.fixture
def 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()
```
### パラメータ付きフィクスチャ
```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
```
### 複数のフィクスチャ使用
```python
@pytest.fixture
def user():
return User(id=1, name="Alice")
@pytest.fixture
def 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)
```
### 自動使用フィクスチャ
```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
```
### 共有フィクスチャ用のConftest.py
```python
# tests/conftest.py
import pytest
@pytest.fixture
def client():
"""Shared fixture for all tests."""
app = create_app(testing=True)
with app.test_client() as client:
yield client
@pytest.fixture
def 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}"}
```
## パラメータ化
### 基本的なパラメータ化
```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
```
### 複数パラメータ
```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
```
### ID付きパラメータ化
```python
@pytest.mark.parametrize("input,expected", [
("valid@email.com", 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
```
### パラメータ化フィクスチャ
```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
```
## マーカーとテスト選択
### カスタムマーカー
```python
# Mark slow tests
@pytest.mark.slow
def test_slow_operation():
time.sleep(5)
# Mark integration tests
@pytest.mark.integration
def test_api_integration():
response = requests.get("https://api.example.com")
assert response.status_code == 200
# Mark unit tests
@pytest.mark.unit
def test_unit_logic():
assert calculate(2, 3) == 5
```
### 特定のテストを実行
```bash
# Run only fast tests
pytest -m "not slow"
# Run only integration tests
pytest -m integration
# Run integration or slow tests
pytest -m "integration or slow"
# Run tests marked as unit but not slow
pytest -m "unit and not slow"
```
### pytest.iniでマーカーを設定
```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
```
## モックとパッチ
### 関数のモック
```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"
```
### 戻り値のモック
```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")
```
### 例外のモック
```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()
```
### コンテキストマネージャのモック
```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"
```
### Autospec使用
```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()
```
### クラスインスタンスのモック
```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()
```
### プロパティのモック
```python
@pytest.fixture
def 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"
```
## 非同期コードのテスト
### pytest-asyncioを使用した非同期テスト
```python
import pytest
@pytest.mark.asyncio
async def test_async_function():
"""Test async function."""
result = await async_add(2, 3)
assert result == 5
@pytest.mark.asyncio
async def test_async_with_fixture(async_client):
"""Test async with async fixture."""
response = await async_client.get("/api/users")
assert response.status_code == 200
```
### 非同期フィクスチャ
```python
@pytest.fixture
async def async_client():
"""Async fixture providing async test client."""
app = create_app()
async with app.test_client() as client:
yield client
@pytest.mark.asyncio
async def test_api_endpoint(async_client):
"""Test using async fixture."""
response = await async_client.get("/api/data")
assert response.status_code == 200
```
### 非同期関数のモック
```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"
```
## 例外のテスト
### 期待される例外のテスト
```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")
```
### 例外属性のテスト
```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)
```
## 副作用のテスト
### ファイル操作のテスト
```python
import tempfile
import 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)
```
### pytestのtmp_pathフィクスチャを使用したテスト
```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
```
### tmpdirフィクスチャを使用したテスト
```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"
```
## テストの整理
### ディレクトリ構造
```
tests/
├── conftest.py # Shared fixtures
├── __init__.py
├── unit/ # Unit tests
│ ├── __init__.py
│ ├── test_models.py
│ ├── test_utils.py
│ └── test_services.py
├── integration/ # Integration tests
│ ├── __init__.py
│ ├── test_api.py
│ └── test_database.py
└── e2e/ # End-to-end tests
├── __init__.py
└── test_user_flow.py
```
### テストクラス
```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)
```
## ベストプラクティス
### すべきこと
- **TDDに従う**: コードの前にテストを書く（赤-緑-リファクタリング）
- **一つのことをテスト**: 各テストは単一の動作を検証すべき
- **説明的な名前を使用**: `test_user_login_with_invalid_credentials_fails`
- **フィクスチャを使用**: フィクスチャで重複を排除
- **外部依存をモック**: 外部サービスに依存しない
- **エッジケースをテスト**: 空の入力、None値、境界条件
- **80%以上のカバレッジを目指す**: クリティカルパスに焦点を当てる
- **テストを高速に保つ**: マークを使用して遅いテストを分離
### してはいけないこと
- **実装をテストしない**: 内部ではなく動作をテスト
- **テストで複雑な条件文を使用しない**: テストをシンプルに保つ
- **テスト失敗を無視しない**: すべてのテストは通過する必要がある
- **サードパーティコードをテストしない**: ライブラリが機能することを信頼
- **テスト間で状態を共有しない**: テストは独立すべき
- **テストで例外をキャッチしない**: `pytest.raises`を使用
- **print文を使用しない**: アサーションとpytestの出力を使用
- **脆弱すぎるテストを書かない**: 過度に具体的なモックを避ける
## 一般的なパターン
### APIエンドポイントのテスト（FastAPI/Flask）
```python
@pytest.fixture
def 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": "alice@example.com"
})
assert response.status_code == 201
assert response.json["name"] == "Alice"
```
### データベース操作のテスト
```python
@pytest.fixture
def 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="alice@example.com")
db_session.add(user)
db_session.commit()
retrieved = db_session.query(User).filter_by(name="Alice").first()
assert retrieved.email == "alice@example.com"
```
### クラスメソッドのテスト
```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設定
### pytest.ini
```ini
[pytest]
testpaths = tests
python_files = test_*.py
python_classes = Test*
python_functions = test_*
addopts =
--strict-markers
--disable-warnings
--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
```
### pyproject.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",
]
```
## テストの実行
```bash
# Run all tests
pytest
# Run specific file
pytest tests/test_utils.py
# Run specific test
pytest tests/test_utils.py::test_function
# Run with verbose output
pytest -v
# Run with coverage
pytest --cov=mypackage --cov-report=html
# Run only fast tests
pytest -m "not slow"
# Run until first failure
pytest -x
# Run and stop on N failures
pytest --maxfail=3
# Run last failed tests
pytest --lf
# Run tests with pattern
pytest -k "test_user"
# Run with debugger on failure
pytest --pdb
```
## クイックリファレンス
| パターン | 使用法 |
|---------|-------|
| `pytest.raises()` | 期待される例外をテスト |
| `@pytest.fixture()` | 再利用可能なテストフィクスチャを作成 |
| `@pytest.mark.parametrize()` | 複数の入力でテストを実行 |
| `@pytest.mark.slow` | 遅いテストをマーク |
| `pytest -m "not slow"` | 遅いテストをスキップ |
| `@patch()` | 関数とクラスをモック |
| `tmp_path`フィクスチャ | 自動一時ディレクトリ |
| `pytest --cov` | カバレッジレポートを生成 |
| `assert` | シンプルで読みやすいアサーション |
**覚えておいてください**: テストもコードです。それらをクリーンで、読みやすく、保守可能に保ちましょう。良いテストはバグをキャッチし、優れたテストはそれらを防ぎます。
## 原文
- [英語版の原文](../../../../skills/python-testing/SKILL.md)
## ナビゲーション
- [日本語ドキュメント一覧](../../README.md)
- [skills/README.md](../README.md)
- [貢献ガイド](../../../../CONTRIBUTING.md)
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