Fixture scope with parallel tests in PyTest - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a fixture with session scope.

PyTest

import pytest

@pytest.fixture(scope=[1])
def setup_db():
    print("Setup DB")
    yield
    print("Teardown DB")

Drag options to blanks, or click blank then click option'

Afunction

Bsession

Cmodule

Dclass

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'function' scope when you want to share setup across tests.

Confusing 'module' and 'session' scopes.

The 'session' scope means the fixture is created once per test session, ideal for expensive setup shared across tests.

2fill in blank

medium

Complete the code to run tests in parallel using pytest-xdist.

PyTest

# Run tests with pytest-xdist
pytest -n [1]

Drag options to blanks, or click blank then click option'

Aauto

B4

Call

Dparallel

Attempts:

3 left

💡 Hint

Common Mistakes

Using invalid values like 'all' or 'parallel' for '-n'.

Not installing pytest-xdist before using '-n'.

Using '-n auto' lets pytest-xdist automatically decide the number of CPUs to use for parallel tests.

3fill in blank

hard

Fix the error in the fixture to avoid sharing state in parallel tests.

PyTest

import pytest

@pytest.fixture(scope="session")
def resource():
    data = []
    yield data
    data.clear()

# Tests modify resource by appending values
# Problem: parallel tests share the same list causing conflicts
# Fix by changing [1]

Drag options to blanks, or click blank then click option'

Ascope to 'module'

Bdata to a global variable

Cyield to return

Dscope to 'function'

Attempts:

3 left

💡 Hint

Common Mistakes

Keeping session scope and causing test interference.

Using global variables which are shared across tests.

Changing the fixture scope to 'function' ensures each test gets its own fresh list, avoiding shared state issues in parallel runs.

4fill in blank

hard

Fill both blanks to create a fixture that runs once per module and uses autouse.

PyTest

@pytest.fixture(scope=[1], autouse=[2])
def setup_env():
    print("Setup environment")
    yield
    print("Teardown environment")

Drag options to blanks, or click blank then click option'

Amodule

Bfunction

CTrue

DFalse

Attempts:

3 left

💡 Hint

Common Mistakes

Setting autouse to False and expecting automatic use.

Using function scope when module scope is needed.

Setting scope to 'module' runs the fixture once per module. Autouse=True makes it run automatically for all tests in the module.

5fill in blank

hard

Fill all three blanks to create a parametrized fixture with session scope and proper teardown.

PyTest

@pytest.fixture(scope=[1], params=["chrome", "firefox"])
def browser(request):
    driver = start_driver([2])
    yield driver
    [3](driver)

Drag options to blanks, or click blank then click option'

Asession

Brequest.param

Cstop_driver

Dfunction

Attempts:

3 left

💡 Hint

Common Mistakes

Using function scope instead of session for sharing.

Not using request.param to get parameter value.

Forgetting to stop the driver in teardown.

Session scope shares the fixture for the session. request.param accesses the current parameter. stop_driver properly closes the driver after test.

Practice

1. What does the scope='session' parameter in a pytest fixture control?

easy

A. The fixture runs once per entire test session.

B. The fixture runs once per test function.

C. The fixture runs once per test class.

D. The fixture runs once per test module.

Solution

1. Step 1: Understand fixture scopes in pytest

   Pytest fixtures can have different scopes like function, class, module, and session, which control how often the fixture setup runs.

2. Step 2: Identify what session scope means

   Session scope means the fixture runs only once for the entire test session, regardless of how many tests use it.

3. Final Answer:

   The fixture runs once per entire test session. -> Option A

4. Quick Check:

   scope='session' = runs once per session [OK]

Hint: Session scope means one setup for all tests in session [OK]

Common Mistakes:

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

2. Which of the following is the correct syntax to define a pytest fixture with session scope?

easy

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

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

C. @pytest.fixture(session=True)

D. @pytest.fixture(scope=session)

Solution

1. Step 1: Recall pytest fixture syntax

   Pytest fixtures use the decorator @pytest.fixture() with optional parameters like scope as a string.

2. Step 2: Identify correct scope parameter usage

   The scope parameter must be a string, so scope='session' is correct. Options C and D are invalid syntax.

3. Final Answer:

   @pytest.fixture(scope='session') -> Option B

4. Quick Check:

   Correct syntax uses scope='session' string [OK]

Hint: Use quotes around scope value: scope='session' [OK]

Common Mistakes:

• Omitting quotes around 'session'
• Using invalid keyword arguments
• Confusing scope with boolean flags

3. Consider this pytest fixture and test code run with 2 parallel workers:

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

def test_a(resource):
    pass

def test_b(resource):
    pass

How many times will 'Setup resource' be printed during the entire test run?

medium

A. Once

B. Zero times

C. Twice

D. Four times

Solution

1. Step 1: Understand session scope with parallel workers

   When running tests in parallel with pytest-xdist, each worker runs its own session, so session-scoped fixtures run once per worker.

2. Step 2: Calculate total setup calls

   With 2 workers, the fixture setup runs once per worker, so 'Setup resource' prints twice.

3. Final Answer:

   Twice -> Option C

4. Quick Check:

   Session scope runs once per worker = 2 times [OK]

Hint: Session scope runs once per worker in parallel tests [OK]

Common Mistakes:

• Assuming session scope runs only once globally
• Ignoring parallel worker count
• Confusing function scope with session scope

4. You have a session-scoped fixture used in parallel tests with 3 workers. You notice the fixture setup runs 3 times, but you want it to run only once globally. What is the likely cause and fix?

medium

A. Cause: fixture is not used; Fix: add fixture to tests.

B. Cause: fixture scope is function; Fix: change to session scope.

C. Cause: parallel tests disabled; Fix: enable parallel execution.

D. Cause: session scope runs per worker; Fix: use a database or external service to share state.

Solution

1. Step 1: Identify why session scope runs multiple times

   In parallel testing, session scope runs once per worker, so with 3 workers, setup runs 3 times.

2. Step 2: Understand how to share fixture state globally

   To run setup only once globally, you must share state outside pytest workers, e.g., via a database or external service.

3. Final Answer:

   Cause: session scope runs per worker; Fix: use a database or external service to share state. -> Option D

4. Quick Check:

   Session scope per worker needs external sharing [OK]

Hint: Session scope runs per worker; share state externally to fix [OK]

Common Mistakes:

• Thinking session scope runs once globally in parallel
• Changing scope to function instead of sharing state
• Ignoring parallel execution effects

5. You want to run expensive setup code only once for all tests across 4 parallel pytest workers. Which approach correctly ensures this behavior?

hard

A. Use scope='session' fixture and implement external resource locking (e.g., file lock or database).

B. Use scope='function' fixture and cache results in a global variable.

C. Use scope='session' fixture and rely on pytest-xdist to share it automatically.

D. Use scope='module' fixture and run tests sequentially.

Solution

1. Step 1: Understand session scope behavior with parallel workers

   Session scope runs once per worker, so with 4 workers, setup runs 4 times unless shared externally.

2. Step 2: Identify how to run setup only once globally

   Implementing external resource locking (like a file lock or database flag) ensures only one worker runs the expensive setup.

3. Final Answer:

   Use scope='session' fixture and implement external resource locking (e.g., file lock or database). -> Option A

4. Quick Check:

   External locking + session scope = single global setup [OK]

Hint: Combine session scope with external locking for global setup [OK]

Common Mistakes:

• Assuming pytest-xdist shares session fixtures automatically
• Using function scope and expecting single setup
• Running tests sequentially defeats parallel purpose