Fixture Scopes

Understanding Fixture Scopes

Fixture scopes control how often a fixture is executed. pytest supports four scopes: function, class, module, and session.

Function Scope (Default)

The fixture runs once per test function. This is the default behavior:

@pytest.fixture(scope="function")
def temp_dir():
    d = create_temp_directory()
    yield d
    cleanup_directory(d)

def test_one(temp_dir):
    # Gets a fresh temp_dir
    assert os.path.exists(temp_dir)

def test_two(temp_dir):
    # Gets a NEW temp_dir (different from test_one)
    assert os.path.exists(temp_dir)

Class Scope

The fixture runs once per test class, shared across all methods in that class:

@pytest.fixture(scope="class")
def database():
    conn = create_connection()
    yield conn
    conn.close()

class TestUserQueries:
    def test_insert(self, database):
        database.execute("INSERT INTO users ...")

    def test_select(self, database):
        # Uses the SAME connection as test_insert
        database.execute("SELECT * FROM users")

Module Scope

The fixture runs once per test file, shared across all tests in that module:

@pytest.fixture(scope="module")
def expensive_computation():
    # This runs only once for the entire file
    return compute_heavy_data()

def test_first(expensive_computation):
    assert expensive_computation is not None

def test_second(expensive_computation):
    # Uses the SAME result (not recomputed)
    assert len(expensive_computation) > 0

Session Scope

The fixture runs once for the entire test session, shared across all files:

@pytest.fixture(scope="session")
def database_connection():
    conn = create_connection()
    yield conn
    conn.close()

# All test files share this single connection