fixture

Learn fixtures with @pytest.fixture.

fixture

A fixture is setup code shared by tests. It builds database connections, sample data or temp files and cleans up when the test ends.

You decorate a function with @pytest.fixture; tests call it by its parameter name. pytest runs the fixture and injects the result into the parameter.

import pytest

@pytest.fixture
def sample_list():
    return [1, 2, 3]

def test_total(sample_list):
    assert sum(sample_list) == 6

This avoids repeated setup and keeps tests short.

Fixture scope

Fixtures run fresh for each test by default (scope="function"). For heavy setup you can change this: scope="module" runs once per module, scope="session" once per session.

@pytest.fixture(scope="module")
def db():
    return open_connection()

A larger scope is faster but watch state sharing: if a test mutates data, later tests are affected. That's why most fixtures stay at function scope.

Exercise Use sample_list with a fixture

Start with import pytest. Decorate sample_list() with @pytest.fixture; it returns [1, 2, 3]. The test function test_total(sample_list) runs assert sum(sample_list) == 6. End with test_total(sample_list()) and print("ok").

Show example solution

import pytest

@pytest.fixture
def sample_list():
    return [1, 2, 3]

def test_total(sample_list):
    assert sum(sample_list) == 6

test_total(sample_list())
print("ok")

Test yourself

How is a fixture used in a test?
- Imported with import
- Assigned as a global variable
- Passed as a parameter to the test function
- Printed with print
Show answer

Passed as a parameter to the test function — pytest injects the fixture result into the parameter with the same name.
Match the fixture concepts

@pytest.fixture

Fixture marker
def sample_list

Fixture definition
test_total(sample_list)

Uses the fixture
scope="module"

Once per module

Add the fixture decorator

import pytest

@____(scope="module")
def db():
    return open_connection()

Show answer

import pytest

@pytest.fixture(scope="module")
def db():
    return open_connection()

Next lesson: parametrize

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