python-testing

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

# 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

pytest --cov=mypackage --cov-report=term-missing --cov-report=html

pytest 基础

基本测试结构

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

# 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

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