# pytest: Python Testing Framework


pytest is a mature, feature-rich testing framework for Python that simplifies test writing and execution through a clear, concise syntax. Unlike Python's built-in unittest module, pytest minimizes boilerplate and offers powerful fixture capabilities, parameterized testing, and a comprehensive plugin ecosystem.

pytest is the standard choice for most Python testing, from small scripts to large applications. Its `assert`-based syntax requires less code than unittest, and its fixture system scales well as projects grow. The main reasons to prefer unittest over pytest are maintaining a codebase already committed to unittest conventions or working in an environment where third-party packages are restricted.

## When to use pytest

Use pytest for any Python project that needs automated tests. Its low-boilerplate syntax and fixture system make it the right default for unit tests, integration tests, and end-to-end tests alike. Prefer pytest over unittest unless the project already uses unittest conventions throughout or third-party packages cannot be installed. For [multi-version test automation](https://pydevtools.com/handbook/explanation/do-you-still-need-tox-or-nox-if-you-use-uv.md), pair pytest with [tox](https://pydevtools.com/handbook/reference/tox.md) or [nox](https://pydevtools.com/handbook/reference/nox.md).

## Core Features

### Test Discovery and Execution

- Automatic discovery of test modules, functions, and methods following naming conventions
- Simple assertion syntax using Python's built-in `assert`
- Detailed failure reports with intelligent introspection and value comparison
- Flexible test selection via command-line options, markers, and path specifications
- Parallel test execution for faster test runs

### Fixtures

Fixtures provide a modular way to manage test dependencies and setup/teardown:

```python
@pytest.fixture
def api_client():
    client = APIClient()
    yield client
    client.close()

def test_api_call(api_client):
    # The fixture is automatically injected
    response = api_client.get_data()
    assert response.status_code == 200
```

Fixtures can be scoped to function, class, module, or session levels.

### Parameterization

Tests can be run with multiple sets of inputs:

```python
@pytest.mark.parametrize("input,expected", [
    (1, 1),
    (2, 4),
    (3, 9),
    (4, 16),
])
def test_square(input, expected):
    assert input * input == expected
```

## Command-Line Interface

```bash
# Run all tests
pytest

# Run tests in a specific file
pytest test_file.py

# Run a specific test
pytest test_file.py::test_function

# Run tests matching a pattern
pytest -k "pattern"

# Run tests with a specific marker
pytest -m slow
```

## Pros

- Minimal boilerplate compared to unittest
- Powerful fixture system for dependency injection
- Extensive plugin ecosystem
- Detailed error reporting
- Compatible with other testing tools

## Cons

- Learning curve for advanced features
- Plugin dependencies can complicate maintenance
- Fixture complexity can grow in large projects
- Some patterns differ from unittest paradigms

## Learn More

- [Setting up testing with pytest and uv](https://pydevtools.com/handbook/tutorial/setting-up-testing-with-pytest-and-uv.md) (Tutorial)
- [How to run tests using uv](https://pydevtools.com/handbook/how-to/how-to-run-tests-using-uv.md)
- [How to test against multiple Python versions using uv](https://pydevtools.com/handbook/how-to/how-to-test-against-multiple-python-versions-using-uv.md)
- [How to fix common pytest errors with uv](https://pydevtools.com/handbook/how-to/how-to-fix-common-pytest-errors-with-uv.md)
- [How to parameterize tests with pytest](https://pydevtools.com/handbook/how-to/how-to-parameterize-tests-with-pytest.md)
- [How to run tests in parallel with pytest-xdist](https://pydevtools.com/handbook/how-to/how-to-run-tests-in-parallel-with-pytest-xdist.md)
- [How to measure code coverage with pytest-cov](https://pydevtools.com/handbook/how-to/how-to-measure-code-coverage-with-pytest-cov.md)
- [How to configure Cursor for pytest](https://pydevtools.com/handbook/how-to/how-to-configure-cursor-for-pytest.md)
- [Essential pytest plugins for reliable, fast test suites](https://pydevtools.com/handbook/explanation/essential-pytest-plugins.md)
- [tox](https://pydevtools.com/handbook/reference/tox.md) and [nox](https://pydevtools.com/handbook/reference/nox.md) for multi-version test automation
- [pytest Documentation](https://docs.pytest.org/)
- [Plugin Directory](https://docs.pytest.org/en/stable/reference/plugin_list.html)
- [Best Practices](https://docs.pytest.org/en/stable/explanation/goodpractices.html)