pytest-writer

Pytest Writer

Overview

Use the pytest framework to write high-quality, maintainable Python test cases. Supports pytest core features such as simple assertions, automatic discovery, fixtures, and parameterized tests.

Quick Start

Basic test structure

# test_sample.py
def inc(x):
    return x + 1

def test_answer():
    assert inc(3) == 4

Run tests:

pytest

Test file naming conventions

• Test files:test_*.py or *_test.py
• Test functions:test_*
• Test classes:Test*

Core Capabilities

1. Write basic tests

Use simple assert statements; pytest provides detailed failure information:

def test_addition():
    assert 1 + 1 == 2

def test_string_operations():
    text = "hello"
    assert text.upper() == "HELLO"
    assert len(text) == 5

2. Use Fixtures

Fixtures are used to manage test resources and dependencies:

import pytest

@pytest.fixture
def sample_data():
    return {"name": "test", "value": 42}

def test_with_fixture(sample_data):
    assert sample_data["value"] == 42

Advanced fixtures usage: see references/fixtures.md

3. Parameterized tests

Use @pytest.mark.parametrize to reduce duplicate code:

@pytest.mark.parametrize("input,expected", [
    (3, 4),
    (5, 6),
    (10, 11),
])
def test_increment(input, expected):
    assert input + 1 == expected

More parameterization patterns: see references/parametrize.md

4. Assertion techniques

Take advantage of pytest's assertion introspection feature:

def test_dict_comparison():
    expected = {"a": 1, "b": 2}
    actual = {"a": 1, "b": 3}
    assert actual == expected  # pytest会显示详细的差异

Assertion best practices: see references/assertions.md

5. Test organization

Organize by functionality

tests/
├── test_auth.py
├── test_database.py
├── test_api.py
└── conftest.py  # 共享fixtures

Use conftest.py

Define shared fixtures in conftest.py:

# conftest.py
@pytest.fixture
def db_connection():
    conn = create_connection()
    yield conn
    conn.close()

6. Exception testing

Use pytest.raises to test exceptions:

def test_zero_division():
    with pytest.raises(ZeroDivisionError):
        1 / 0

def test_value_error():
    with pytest.raises(ValueError) as exc_info:
        int("invalid")
    assert "invalid literal" in str(exc_info.value)

7. Skipping and expected failures

@pytest.mark.skip(reason="功能未实现")
def test_not_implemented():
    pass

@pytest.mark.skipif(sys.version_info < (3, 8), reason="需要Python 3.8+")
def test_python38_feature():
    pass

@pytest.mark.xfail
def test_known_failure():
    assert False  # 预期失败

Testing Best Practices

Test naming

• Use descriptive test names:test_user_login_with_valid_credentials
• Follow the AAA pattern: Arrange → Act → Assert

def test_calculate_total_with_discount():
    # Arrange
    cart = Cart(items=[Item(price=100), Item(price=50)])
    discount = 0.1
    
    # Act
    total = cart.calculate_total(discount)
    
    # Assert
    assert total == 135

Test isolation

• Each test should run independently
• Use fixtures to ensure isolation between tests
• Avoid dependencies between tests

More best practices: see references/best-practices.md

Running Tests

Basic commands

# 运行所有测试
pytest

# 运行特定文件
pytest tests/test_auth.py

# 运行特定测试函数
pytest tests/test_auth.py::test_login

# 运行匹配模式的测试
pytest -k "login"

# 显示详细输出
pytest -v

# 显示print语句输出
pytest -s

# 在第一个失败时停止
pytest -x

# 运行上次失败的测试
pytest --lf

Test coverage

# 生成覆盖率报告
pytest --cov=src

# 生成HTML报告
pytest --cov=src --cov-report=html

Debugging Failed Tests

View detailed error information

pytest -v --tb=long

Debug with pdb

def test_debugging():
    import pdb; pdb.set_trace()
    result = complex_calculation()
    assert result == expected

Or on the command line:

pytest --pdb

Resources

references/

Detailed reference documentation:

• fixtures.md - complete fixtures usage, scopes, parameterized fixtures
• parametrize.md - various patterns and techniques for parameterized tests
• assertions.md - assertion techniques, custom assertion messages
• best-practices.md - best practices such as test organization, naming conventions, and test isolation

assets/

• test_template.py - standard test file templates, including common patterns and structures