Python pytest fixtures and parameterize patterns

Need reusable test setup, teardown, and data-driven tests in pytest.

Key pytest patterns:

import pytest

# Fixture with setup and teardown
@pytest.fixture
def db_connection():
    conn = create_connection()
    yield conn  # Test runs here
    conn.close()  # Teardown

# Fixture with scope (shared across module)
@pytest.fixture(scope='module')
def app_client():
    app = create_app(testing=True)
    return app.test_client()

# Parameterized tests
@pytest.mark.parametrize('input,expected', [
    ('hello', 'HELLO'),
    ('world', 'WORLD'),
    ('', ''),
])
def test_uppercase(input, expected):
    assert input.upper() == expected

# Fixture that uses another fixture
@pytest.fixture
def authenticated_client(app_client):
    app_client.post('/login', data={'user': 'test'})
    return app_client

# tmp_path fixture (built-in)
def test_file_write(tmp_path):
    f = tmp_path / 'test.txt'
    f.write_text('hello')
    assert f.read_text() == 'hello'

Fixtures provide dependency injection for tests, making setup reusable and teardown automatic.

Python testing with pytest