pytest vs unittest

Comparisons · Reference cheat sheet

📋 Overview

pytest is the common default for modern Python tests (fixtures, parametrize, assert rewriting). unittest is the stdlib xUnit-style framework — fine for stdlib-only environments and legacy suites.

🔧 Core concepts

When to use pytest: almost all application and library projects.

When to use unittest: zero-dependency constraints, teaching stdlib, or extending large existing unittest suites.

💡 Examples

pytest:

import pytest

@pytest.fixture
def n():
    return 2

@pytest.mark.parametrize("x,y", [(1, 2), (2, 4)])
def test_double(x, y, n):
    assert x * n == y

unittest:

import unittest

class DoubleTest(unittest.TestCase):
    def test_double(self):
        self.assertEqual(2 * 2, 4)

if __name__ == "__main__":
    unittest.main()

⚠️ Pitfalls

• Mixing styles in one repo without guidance confuses contributors — pick a default.
• pytest plugin overload can obscure failures — keep conftest lean.
• unittest mock (unittest.mock) works great with pytest too.

🔗 Related

• Pytest/
• Python/getting_started.md
• README.md