Pytest

pytest Testing Framework

pytest is a mature, full-featured Python testing framework that makes it easy to write small, readable tests that can scale to support complex functional testing.

Quick Start

Installation

pip install -U pytest
pytest --version

Basic Test

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

def test_answer():
    assert inc(3) == 5

Run with pytest - it auto-discovers test_*.py and *_test.py files.

Test Discovery Rules

• Files: test_*.py or *_test.py
• Functions: test_ prefix outside classes
• Classes: Test prefix (no __init__)
• Methods: test_ prefix in Test classes

Core Concepts

Fixtures

Fixtures provide fixed baseline for tests:

import pytest

@pytest.fixture
def smtp_connection():
    return smtplib.SMTP("smtp.gmail.com", 587, timeout=5)

def test_ehlo(smtp_connection):
    response, msg = smtp_connection.ehlo()
    assert response == 250

Scopes: function (default), class, module, package, session

Parametrization

Run same test with multiple inputs:

@pytest.mark.parametrize("input,expected", [
    ("3+5", 8),
    ("2+4", 6),
    pytest.param("6*9", 42, marks=pytest.mark.xfail),
])
def test_eval(input, expected):
    assert eval(input) == expected

Markers

@pytest.mark.skip(reason="not implemented")
@pytest.mark.skipif(sys.platform == "win32", reason="linux only")
@pytest.mark.xfail(reason="known bug")
@pytest.mark.slow  # custom marker
def test_something():
    pass

Run by marker: pytest -m slow

Assertions

# Basic assert with introspection
assert func(3) == 5

# Exception testing
with pytest.raises(ValueError, match="invalid"):
    raise ValueError("invalid input")

# Floating point comparison
assert 0.1 + 0.2 == pytest.approx(0.3)

# Warnings
with pytest.warns(UserWarning):
    warnings.warn("hello", UserWarning)

CLI Reference

pytest                           # run all tests
pytest test_mod.py               # specific file
pytest tests/                    # directory
pytest -k "MyClass and not method"  # keyword filter
pytest -m slow                   # by marker
pytest -x                        # stop on first failure
pytest -v                        # verbose
pytest -s                        # show stdout
pytest --tb=short                # shorter traceback
pytest --fixtures                # list fixtures
pytest --collect-only            # show tests without running
pytest -n 4                      # parallel (needs pytest-xdist)

Documentation Index

Getting Started

• getting-started.md - Installation, first test, grouping tests, temporary directories

How-To Guides

Testing Basics:

• how-to/usage.md - Invoking pytest, selecting tests, CLI options
• how-to/assert.md - Assertions, exceptions, warnings, approx comparisons
• how-to/fixtures.md - Complete fixture guide: scopes, teardown, parametrization, factories
• how-to/parametrize.md - Parametrizing tests and fixtures
• how-to/mark.md - Custom markers, registering marks
• how-to/skipping.md - skip, skipif, xfail markers

Test Organization:

• how-to/tmp_path.md - Temporary directories and files
• how-to/monkeypatch.md - Monkeypatching for testing
• how-to/cache.md - Caching values across test runs
• how-to/doctest.md - Running doctests with pytest

Output & Capture:

• how-to/capture-stdout-stderr.md - Capturing output
• how-to/capture-warnings.md - Capturing warnings
• how-to/logging.md - Logging during tests
• how-to/output.md - Managing test output
• how-to/failures.md - Handling test failures

Integration:

• how-to/unittest.md - Running unittest tests
• how-to/existingtestsuite.md - Migrating existing test suites
• how-to/xunit_setup.md - xUnit-style setup/teardown
• how-to/subtests.md - Subtest support

Plugins:

• how-to/plugins.md - Using pytest plugins
• how-to/writing_plugins.md - Writing plugins
• how-to/writing_hook_functions.md - Hook functions

Other:

• how-to/bash-completion.md - Bash completion setup

Reference

• reference/reference.md - Complete API reference
• reference/fixtures.md - Built-in fixtures reference
• reference/customize.md - Configuration and customization
• reference/exit-codes.md - Exit codes reference
• reference/plugin_list.md - Plugin list

Explanation

• explanation/fixtures.md - Fixture concepts explained
• explanation/anatomy.md - Anatomy of a test
• explanation/goodpractices.md - Best practices, project layout, import modes
• explanation/flaky.md - Dealing with flaky tests
• explanation/ci.md - CI integration
• explanation/pythonpath.md - Python path handling
• explanation/types.md - Type annotations in pytest

Examples

• example/simple.md - Simple test examples
• example/parametrize.md - Parametrization examples
• example/markers.md - Marker examples
• example/pythoncollection.md - Collection examples
• example/customdirectory.md - Custom directory layouts
• example/nonpython.md - Non-Python tests
• example/reportingdemo.md - Reporting demonstration
• example/special.md - Special use cases

Common Patterns

conftest.py

Share fixtures across test files:

# tests/conftest.py
import pytest

@pytest.fixture
def database():
    db = Database()
    yield db
    db.close()

Yield Fixture (Teardown)

@pytest.fixture
def resource():
    r = acquire_resource()
    yield r
    release_resource(r)  # teardown

Fixture Factories

@pytest.fixture
def make_customer():
    created = []
    def _make(name):
        c = Customer(name)
        created.append(c)
        return c
    yield _make
    for c in created:
        c.delete()

Autouse Fixtures

@pytest.fixture(autouse=True)
def clean_db(db):
    yield
    db.rollback()

Configuration

pyproject.toml

[pytest]
testpaths = ["tests"]
python_files = ["test_*.py"]
python_classes = ["Test*"]
python_functions = ["test_*"]
addopts = "-v --tb=short"
markers = [
    "slow: marks tests as slow",
    "integration: integration tests",
]

pytest.ini

[pytest]
testpaths = tests
addopts = -v

Official Resources

• Documentation: https://docs.pytest.org/
• PyPI: https://pypi.org/project/pytest/
• GitHub: https://github.com/pytest-dev/pytest/

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