Async fixtures (pytest-asyncio) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of async fixture usage in pytest

What is the output of running this pytest test with an async fixture?

PyTest

import pytest
import asyncio

@pytest.fixture
async def async_resource():
    await asyncio.sleep(0.1)
    return 'resource_ready'

@pytest.mark.asyncio
async def test_async_fixture(async_resource):
    assert async_resource == 'resource_ready'
    print(async_resource)

A Test fails with AssertionError

B Test passes and prints 'resource_ready'

C Test raises RuntimeError due to event loop

D Test is skipped due to missing marker

💡 Hint

Remember that pytest-asyncio supports async fixtures and test functions with the @pytest.mark.asyncio decorator.

The async fixture 'async_resource' awaits a short sleep and returns a string. The test uses this fixture and asserts the returned value. Since the fixture and test are properly async and marked, the test passes and prints the string.

❓ assertion

intermediate

Correct assertion for async fixture return value

Given an async fixture that returns a dictionary {'status': 'ok', 'code': 200}, which assertion correctly verifies the 'code' key in a pytest async test?

PyTest

import pytest

@pytest.fixture
async def api_response():
    return {'status': 'ok', 'code': 200}

@pytest.mark.asyncio
async def test_api_code(api_response):
    # Which assertion is correct here?
    pass

A assert api_response['code'] == 200

B assert api_response['code'] != 200

C assert api_response.get('code') is '200'

D assert api_response.code == 200

💡 Hint

Dictionaries use bracket notation to access keys, and '==' compares values correctly.

Option A correctly accesses the dictionary key 'code' and compares it to the integer 200. Option A is invalid because dictionaries do not support attribute access. Option A compares with 'is' and a string, which is incorrect. Option A asserts the opposite of the expected value.

🔧 Debug

advanced

Identify the cause of RuntimeError in async fixture test

Why does this pytest async test raise RuntimeError: This event loop is already running?

PyTest

import pytest
import asyncio

@pytest.fixture
async def async_data():
    await asyncio.sleep(0.1)
    return 42

def test_sync_using_async_fixture(async_data):
    assert async_data == 42

A The fixture does not return a coroutine

B The fixture is missing @pytest.mark.asyncio decorator

C The test function is not async and tries to use an async fixture synchronously

D The test function is missing a call to asyncio.run()

💡 Hint

Async fixtures must be used in async test functions or with proper event loop management.

The test function is synchronous but uses an async fixture. Pytest tries to run the async fixture in the current event loop, which is already running, causing the RuntimeError. Making the test async or using pytest-asyncio marker fixes this.

🧠 Conceptual

advanced

Purpose of async fixtures in pytest-asyncio

What is the main benefit of using async fixtures in pytest-asyncio?

A They allow setup and teardown code to run asynchronously, improving test performance when dealing with async resources

B They automatically convert synchronous fixtures to async functions

C They enable running tests without an event loop

D They replace the need for mocking in tests

💡 Hint

Think about why async code needs async setup and cleanup.

Async fixtures let you write setup and teardown code that uses await, which is useful for async resources like network calls or databases. This can make tests faster and more realistic. They do not convert sync fixtures or remove the need for mocking.

❓ framework

expert

Correct pytest-asyncio fixture and test integration

Which option shows the correct way to define and use an async fixture with pytest-asyncio to test an async function that returns 'done' after a delay?

PyTest

import pytest
import asyncio

async def async_func():
    await asyncio.sleep(0.05)
    return 'done'

# Choose the correct fixture and test code

A

@pytest.fixture
def fixture_func():
    return asyncio.run(async_func())

@pytest.mark.asyncio
def test_func(fixture_func):
    assert fixture_func == 'done'

B

@pytest.fixture
async def fixture_func():
    return async_func()

def test_func(fixture_func):
    assert fixture_func == 'done'

C

@pytest.fixture
async def fixture_func():
    result = async_func()
    return result

@pytest.mark.asyncio
async def test_func(fixture_func):
    assert await fixture_func == 'done'

D

@pytest.fixture
async def fixture_func():
    result = await async_func()
    return result

@pytest.mark.asyncio
async def test_func(fixture_func):
    assert fixture_func == 'done'

💡 Hint

Async fixtures must await async calls and tests must be async with the marker.

Option D correctly awaits async_func inside the async fixture and returns the awaited result. The test is async and uses the fixture value directly. Option D returns a coroutine without awaiting, and test is sync, causing errors. Option D uses asyncio.run inside a sync fixture, which is discouraged and test is sync with marker mismatch. Option D returns coroutine without await in fixture and tries to await in test, which is invalid.