pytest — The Python Testing Framework That Scales

pip install pytest

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

def test_add():
    assert add(1, 2) == 3

def test_add_negative():
    assert add(-1, -2) == -3

def test_add_strings():
    assert add("hello ", "world") == "hello world"

pytest                       # Auto-discover and run tests
pytest -v                    # Verbose
pytest -x                    # Stop on first failure
pytest -k "negative"         # Filter by name pattern
pytest --cov=mypackage       # Coverage (needs pytest-cov)
pytest -n auto               # Parallel (needs pytest-xdist)

Fixtures:

import pytest

@pytest.fixture
def db_session():
    session = create_session()
    yield session
    session.rollback()
    session.close()

def test_create_user(db_session):
    user = User(name="William")
    db_session.add(user)
    db_session.flush()
    assert user.id is not None

@pytest.mark.parametrize("a,b,expected", [(1,2,3), (0,0,0), (-1,1,0)])
def test_add_parametrized(a, b, expected):
    assert add(a, b) == expected