Install

Pytest · Reference cheat sheet

📋 Overview

pytest is the standard Python test runner: discovery, fixtures, asserts, plugins. Install into a venv; optional extras cover coverage, Django, asyncio, and xdist.

🔧 Core concepts

Discovery: test_*.py, *_test.py, Test* classes, test_* functions.

💡 Examples

Install:

python -m venv .venv
source .venv/bin/activate  # Windows: .venv\Scripts\activate
python -m pip install -U pip
python -m pip install pytest pytest-cov

Minimal test:

# tests/test_math.py
def test_add():
    assert 1 + 1 == 2

Run:

pytest
pytest -q
pytest tests/test_math.py::test_add
pytest -k "add and not slow"

pyproject.toml:

[project.optional-dependencies]
dev = ["pytest>=8.0", "pytest-cov>=5.0"]

[tool.pytest.ini_options]
testpaths = ["tests"]
pythonpath = ["src"]
addopts = "-ra"

⚠️ Pitfalls

• Running system pytest outside the venv → wrong packages.
• Putting tests next to app without pythonpath / src layout.
• Naming files test.py only — discovery still works but prefer packages.
• Mixing unittest discovery expectations with pytest layout.
• Forgetting __init__.py when import paths need packages (often optional).

🔗 Related

• Configuration
• CLI
• Fixtures
• Plugins
• Coverage
• xdist