Testing Basics

Pytest · Reference cheat sheet

📋 Overview

Pytest discovers and runs tests with rich asserts, fixtures, and plugins. Name files test_*.py / *_test.py, functions test_*. Prefer small focused tests; use fixtures for shared setup.

🔧 Core concepts

Layers: unit (pure functions), integration (DB/HTTP), e2e (browser — Playwright).

💡 Examples

Minimal test:

# test_math.py
def add(a, b):
    return a + b

def test_add():
    assert add(2, 3) == 5

Run:

pytest -q
pytest tests/test_api.py -k auth
pytest -m "not slow"

Fixture sketch:

import pytest

@pytest.fixture
def client():
    return {"token": "test-token"}

def test_uses_client(client):
    assert client["token"]

⚠️ Pitfalls

• Don't share mutable state between tests without fixtures + scope care.
• Over-mocking hides real bugs — mock at boundaries.
• Huge conftest.py becomes hard to reason about — split by package.

🔗 Related

• Fixtures
• Asserts
• API testing
• Auth testing
• Parametrize