Conftest fixtures (shared across files) in PyTest - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of shared fixture usage across test files

Given the following conftest.py fixture and two test files, what will be the output when running all tests?

PyTest

## conftest.py
import pytest

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

## test_file1.py

def test_one(resource):
    assert resource == 'resource_data'

## test_file2.py

def test_two(resource):
    assert resource == 'resource_data'

A Setup resource\nSetup resource\nTeardown resource\nTeardown resource

B Setup resource\nTeardown resource

C Setup resource\nTeardown resource\nTeardown resource

D Setup resource\nTeardown resource\nSetup resource\nTeardown resource

💡 Hint

Think about the scope='module' fixture and how many times it runs across multiple test files.

A fixture with scope='module' runs once per test module. Since conftest.py is shared, and there are two separate test files (modules), the fixture runs once per test file: setup and teardown for test_file1.py, then for test_file2.py. The output is Setup resource\nTeardown resource\nSetup resource\nTeardown resource.

❓ assertion

intermediate

Correct assertion for fixture data modification

A conftest fixture returns a list. A test modifies the list by appending an item. Which assertion correctly verifies the list content inside the test?

PyTest

import pytest

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

def test_append(sample_list):
    sample_list.append(4)
    # Which assertion is correct here?

A assert sample_list == [4, 1, 2, 3]

B assert sample_list == [1, 2, 3, 4]

C assert sample_list != [1, 2, 3, 4]

D assert sample_list is [1, 2, 3, 4]

💡 Hint

Remember how list append works and how to compare lists in Python.

The append method adds the element at the end of the list, so the list becomes [1, 2, 3, 4]. The correct way to check list equality is using '=='. Using 'is' checks identity, which is not correct here. The order matters, so [4, 1, 2, 3] is incorrect.

🔧 Debug

advanced

Identify the cause of fixture not being shared

You have a fixture in conftest.py with scope='session', but it seems to run before every test function instead of once per session. What is the most likely cause?

PyTest

## conftest.py
import pytest

@pytest.fixture(scope='session')
def db_connection():
    print('Connecting to DB')
    yield 'db_conn'
    print('Closing DB')

## test_module.py

def test_a(db_connection):
    assert db_connection == 'db_conn'

def test_b(db_connection):
    assert db_connection == 'db_conn'

A The fixture is defined in conftest.py but tests are run with '-k' option filtering only one test at a time.

B The fixture is not imported in test_module.py, so it runs multiple times.

C The fixture scope='session' is ignored if tests are in different files.

D The fixture uses yield, which forces it to run before every test.

💡 Hint

Think about how pytest runs tests and how filtering affects fixture scope.

When pytest runs tests with '-k' or other filters that select individual tests, it may create separate sessions for each run, causing session-scoped fixtures to run multiple times. The fixture is correctly defined and shared, but the test run method causes multiple runs.

❓ framework

advanced

Best practice for fixture sharing in large projects

In a large pytest project with many test files, where should you place fixtures that need to be shared across multiple test files?

A Put all fixtures in a separate Python module and import them manually in each test file.

B Define fixtures inside each test file that uses them to avoid conflicts.

C Place shared fixtures in a conftest.py file at the root or common directory.

D Define fixtures inside test classes to scope them to tests only.

💡 Hint

Think about pytest's automatic fixture discovery.

Pytest automatically discovers fixtures defined in conftest.py files in the directory tree. Placing shared fixtures in conftest.py at a common root allows all tests below to use them without imports. Defining fixtures inside test files or classes limits sharing. Manual imports are possible but less convenient.

🧠 Conceptual

expert

Understanding fixture scope and autouse behavior

Consider a fixture in conftest.py defined with scope='function' and autouse=True. How many times will this fixture run if you have 3 test functions in 2 different test files?

A 3 times total, once per test function across all files.

B 6 times total, once per test function in each file separately.

C Once per test file, so 2 times total.

D Once per test session, so only 1 time.

💡 Hint

Remember what scope='function' and autouse=True mean for fixture execution.

A fixture with scope='function' runs before each test function. Autouse=True means it runs automatically without needing to be requested. There are 3 test functions total across the 2 files, so it runs 3 times.