Fixture scope (function, class, module, session) in PyTest

Introduction

Fixture scope controls how often a setup code runs in tests. It helps save time by reusing setup steps when possible.

When you want to run setup before each test function to keep tests independent.

When you want to run setup once per test class to share setup among its tests.

When you want to run setup once per module to share setup among all tests in a file.

When you want to run setup once per test session to share setup across all tests in a run.

When you want to speed up tests by avoiding repeated setup steps.

Syntax

PyTest

@pytest.fixture(scope='function' or 'class' or 'module' or 'session')
def fixture_name():
    # setup code
    yield resource
    # teardown code

The scope parameter defines how often the fixture runs.

Default scope is function, meaning it runs before each test function.

Examples

Runs setup and teardown before and after each test function.

PyTest

@pytest.fixture(scope='function')
def setup_function():
    print('Setup for each test')
    yield
    print('Teardown for each test')

Runs setup once before all tests in a class and teardown after all tests in that class.

PyTest

@pytest.fixture(scope='class')
def setup_class():
    print('Setup once per test class')
    yield
    print('Teardown once per test class')

Runs setup once before all tests in a file and teardown after all tests in that file.

PyTest

@pytest.fixture(scope='module')
def setup_module():
    print('Setup once per module')
    yield
    print('Teardown once per module')

Runs setup once before all tests in the entire run and teardown after all tests finish.

PyTest

@pytest.fixture(scope='session')
def setup_session():
    print('Setup once per test session')
    yield
    print('Teardown once per test session')

Sample Program

This test shows two fixtures with different scopes. The function-scoped fixture runs before and after each test. The class-scoped fixture runs once before all tests in the class and once after.

PyTest

import pytest

@pytest.fixture(scope='function')
def resource_function():
    print('Setup function')
    yield 'resource'
    print('Teardown function')

@pytest.fixture(scope='class')
def resource_class():
    print('Setup class')
    yield 'resource'
    print('Teardown class')

class TestExample:
    def test_one(self, resource_function, resource_class):
        print('Test one running')
        assert resource_function == 'resource'
        assert resource_class == 'resource'

    def test_two(self, resource_function, resource_class):
        print('Test two running')
        assert resource_function == 'resource'
        assert resource_class == 'resource'

Important Notes

Use function scope for isolated tests that need fresh setup each time.

Use wider scopes like class, module, or session to speed up tests by sharing setup.

Remember teardown runs in reverse order of setup.

Summary

Fixture scope controls how often setup and teardown run.

Scopes: function (each test), class (each test class), module (each file), session (whole run).

Choosing the right scope saves time and keeps tests reliable.

Practice

1. What does the function scope mean for a pytest fixture?

easy

A. The fixture runs once per entire test session.

B. The fixture runs once per test class.

C. The fixture runs once per test module.

D. The fixture runs once per test function.

Solution

1. Step 1: Understand fixture scopes

   Pytest fixtures can have different scopes controlling how often they run.

2. Step 2: Define function scope meaning

   Function scope means the fixture runs before each test function and tears down after it.

3. Final Answer:

   The fixture runs once per test function. -> Option D

4. Quick Check:

   function scope = runs per test function [OK]

Hint: Function scope means run before every test function [OK]

Common Mistakes:

• Confusing function scope with class or module scope
• Thinking function scope runs once per class
• Assuming function scope runs once per session

2. Which of the following is the correct way to set a pytest fixture with module scope?

easy

A. @pytest.fixture(scope='module')

B. @pytest.fixture(scope='function')

C. @pytest.fixture(scope='class')

D. @pytest.fixture(scope='session')

Solution

1. Step 1: Recall fixture scope syntax

   To set a fixture scope, use @pytest.fixture(scope='scope_name').

2. Step 2: Match scope name for module

   The correct scope name for module is 'module'.

3. Final Answer:

   @pytest.fixture(scope='module') -> Option A

4. Quick Check:

   module scope syntax = scope='module' [OK]

Hint: Use scope='module' to run fixture once per file [OK]

Common Mistakes:

• Using 'session' instead of 'module' for module scope
• Forgetting to add scope parameter
• Using incorrect quotes or misspelling scope

3. Given this pytest code snippet, how many times will setup_db run?

import pytest

@pytest.fixture(scope='class')
def setup_db():
    print('Setup DB')

class TestA:
    def test_1(self, setup_db):
        pass
    def test_2(self, setup_db):
        pass

class TestB:
    def test_3(self, setup_db):
        pass

medium

A. 1 time

B. 3 times

C. 2 times

D. 4 times

Solution

1. Step 1: Understand class scope behavior

   Fixture with class scope runs once per test class, before any tests in that class.

2. Step 2: Count test classes using the fixture

   There are two test classes: TestA and TestB, each uses setup_db fixture.

3. Step 3: Calculate total runs

   setup_db runs once for TestA and once for TestB, total 2 times.

4. Final Answer:

   2 times -> Option C

5. Quick Check:

   class scope = once per class, 2 classes = 2 runs [OK]

Hint: Class scope runs once per test class [OK]

Common Mistakes:

• Counting runs per test method instead of per class
• Confusing class scope with function scope
• Ignoring multiple test classes

4. Identify the error in this pytest fixture usage:

import pytest

@pytest.fixture(scope='modul')
def setup_env():
    pass

def test_example(setup_env):
    assert True

medium

A. Missing @pytest.mark.usefixtures decorator.

B. Typo in scope value causes fixture not to run.

C. Fixture function must return a value.

D. Test function missing parentheses.

Solution

1. Step 1: Check fixture scope spelling

   The scope value 'modul' is misspelled; correct is 'module'.

2. Step 2: Understand effect of typo

   Pytest will not recognize the scope and may default or error, causing fixture not to run properly.

3. Final Answer:

   Typo in scope value causes fixture not to run. -> Option B

4. Quick Check:

   Scope must be spelled correctly [OK]

Hint: Check scope spelling carefully to avoid errors [OK]

Common Mistakes:

• Assuming fixture must return a value
• Confusing fixture decorator with marker
• Ignoring spelling errors in parameters

5. You want a pytest fixture to initialize a database connection once before all tests in multiple modules run, and close it after all tests finish. Which scope should you use and why?

hard

A. Use session scope to share across all tests in the run.

B. Use function scope to isolate each test.

C. Use module scope to share per file.

D. Use class scope to share per test class.

Solution

1. Step 1: Understand the requirement

   The database connection should be initialized once before all tests in multiple modules and closed after all tests.

2. Step 2: Match scope to requirement

   Session scope runs once per entire test session, perfect for setup/teardown across all modules.

3. Final Answer:

   Use session scope to share across all tests in the run. -> Option A

4. Quick Check:

   Session scope = once per test run [OK]

Hint: Session scope runs once for all tests in the run [OK]

Common Mistakes:

• Choosing function or class scope which run too often
• Using module scope which limits to one file
• Not matching scope to resource lifetime