Testing with pytest⚓︎

What is pytest?⚓︎

pytest is a powerful, flexible, and easy-to-use testing framework for Python. It's designed to make testing simple and scalable, with features that make it easy to write and maintain tests.

Why Use pytest?⚓︎

• Simple: Easy to get started
• Powerful: Rich ecosystem of plugins
• Flexible: Multiple ways to organize tests
• Informative: Detailed failure reports
• Extensible: Large plugin ecosystem

Project Structure⚓︎

my_project/
├── my_package/
│   ├── __init__.py
│   ├── main.py
│   ├── users/
│   │   ├── __init__.py
│   │   ├── models.py
│   │   └── services.py
│   └── orders/
│       ├── __init__.py
│       ├── models.py
│       └── services.py
├── tests/
│   ├── __init__.py
│   ├── conftest.py
│   ├── test_main.py
│   ├── users/
│   │   ├── __init__.py
│   │   ├── test_models.py
│   │   └── test_services.py
│   └── orders/
│       ├── __init__.py
│       ├── test_models.py
│       └── test_services.py
├── pyproject.toml
└── README.md

Getting Started⚓︎

Installation⚓︎

pip install pytest
# or
uv pip install pytest

Basic Test Example⚓︎

# tests/test_main.py
def test_addition():
    assert 1 + 1 == 2

def test_string_operations():
    assert "hello" + " world" == "hello world"

Running Tests⚓︎

# Run all tests
pytest

# Run specific test file
pytest tests/test_main.py

# Run specific test
pytest tests/test_main.py::test_addition

# Run with verbose output
pytest -v

# Run with print statements
pytest -s

Key Features⚓︎

Fixtures⚓︎

# tests/conftest.py
import pytest

@pytest.fixture
def sample_data():
    return {"key": "value"}

# tests/test_main.py
def test_with_fixture(sample_data):
    assert sample_data["key"] == "value"

Parametrize Tests⚓︎

@pytest.mark.parametrize("input,expected", [
    (1, 2),
    (2, 4),
    (3, 6),
])
def test_double(input, expected):
    assert input * 2 == expected

Markers⚓︎

@pytest.mark.slow
def test_slow_operation():
    # This test will be skipped unless explicitly run
    pass

# Run only slow tests
pytest -m slow

Best Practices⚓︎

Test Organization⚓︎

• Keep tests in a separate tests directory
• Mirror your source code structure
• Use conftest.py for shared fixtures

Test Naming⚓︎

• Use descriptive test names
• Follow the pattern test_<function>_<scenario>
• Make test names readable

Test Structure⚓︎

• Arrange-Act-Assert pattern
• One assertion per test
• Keep tests independent

Fixtures⚓︎

• Use fixtures for setup and teardown
• Keep fixtures focused and reusable
• Use conftest.py for shared fixtures

Test Coverage⚓︎

• Aim for high coverage
• Focus on critical paths
• Don't test implementation details

Common pytest Plugins⚓︎

• pytest-cov: Coverage reporting
• pytest-xdist: Parallel test execution
• pytest-mock: Mocking support
• pytest-asyncio: Async test support
• pytest-bdd: Behavior-driven development

Configuration⚓︎

Add to your pyproject.toml:

[tool.pytest.ini_options]
testpaths = ["tests"]
python_files = ["test_*.py"]
addopts = "-v --cov=src"