Fixture scope (function, class, module, session) in PyTest - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the 'function' scope mean in pytest fixtures?

The fixture is created and destroyed for each test function that uses it. It runs fresh for every test.

beginner

Explain the 'class' scope for pytest fixtures.

The fixture is created once per test class and shared among all test methods in that class.

intermediate

What happens when a fixture has 'module' scope?

The fixture is created once per module (file) and shared by all tests in that module.

intermediate

Describe the 'session' scope in pytest fixtures.

The fixture is created once for the entire test session and shared by all tests across all modules.

intermediate

Why would you use a 'session' scoped fixture instead of a 'function' scoped one?

To save time by setting up expensive resources only once for all tests, like a database connection.

Which pytest fixture scope creates a new fixture instance for each test function?

A function

B class

C module

D session

The 'function' scope means the fixture is set up and torn down for every test function.

If you want a fixture to be shared by all tests in a single Python file, which scope should you use?

A function

B class

C module

D session

The 'module' scope shares the fixture across all tests in the same file.

What is the scope that shares a fixture across all test classes and functions in the entire test run?

A session

B function

C module

D class

The 'session' scope creates the fixture once for the whole test session.

Which scope would be best for a fixture that sets up a database connection used by many tests?

A function

B session

C class

D module

Using 'session' scope avoids reconnecting to the database for every test, saving time.

A fixture with 'class' scope is created how many times per test class?

A Once per session

B Once per test function

C Once per module

D Once per test class

The 'class' scope means the fixture is created once for each test class.

Describe the differences between the four pytest fixture scopes: function, class, module, and session.

Think about how often the fixture is created and shared.

Explain a real-life scenario where using a 'session' scoped fixture is better than a 'function' scoped fixture.

Imagine setting up something costly once instead of many times.

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