python-testing

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# 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：

1. **红**：为期望的行为编写一个失败的测试
2. **绿**：编写最少的代码使测试通过
3. **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=html
```

## pytest 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
# 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"
```

## 夹具

### 基本夹具使用

```python
import pytest

@pytest.fixture
def sample_data():
    """Fixture providing sample data."""

From Luohaothu/everything-codex, MIT.

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