Context manager fixtures in PyTest - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a pytest fixture using a context manager.

PyTest

import pytest

@pytest.fixture
 def resource():
     with [1]() as res:
         yield res

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

Aresource_manager

Bopen_resource

Ccontextlib.contextmanager

Dsetup_resource

Attempts:

3 left

💡 Hint

Common Mistakes

Using a function that is not a context manager.

Forgetting to use 'with' statement.

Yielding without a context manager.

The fixture uses a context manager called 'resource_manager' to manage the resource lifecycle.

2fill in blank

medium

Complete the code to use the fixture in a test function.

PyTest

def test_example([1]):
    assert resource.is_active()

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

Acontext

Bsetup

Cresource

Dmanager

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different argument name than the fixture.

Not passing the fixture as a parameter.

The test function receives the fixture named 'resource' as an argument to use it.

3fill in blank

hard

Fix the error in the fixture to properly close the resource after the test.

PyTest

import pytest

@pytest.fixture
 def resource():
     res = open_resource()
     yield res
     [1]

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

Ares.cleanup()

Bres.open()

Cclose(res)

Dres.close()

Attempts:

3 left

💡 Hint

Common Mistakes

Calling open() instead of close().

Using a non-existent cleanup method.

Not closing the resource at all.

After yielding the resource, calling 'res.close()' ensures proper cleanup.

4fill in blank

hard

Fill both blanks to create a fixture that uses contextlib.contextmanager.

PyTest

import pytest
import contextlib

@[1]
def resource():
    @contextlib.[2]
    def manager():
        print('setup')
        yield 'resource'
        print('teardown')
    return manager()

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

Afixture

Bcontextmanager

Ccontextmanager_decorator

Dfixture_decorator

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up decorators.

Using incorrect decorator names.

Not returning the context manager.

The fixture is decorated with '@pytest.fixture' and the inner function with '@contextlib.contextmanager'.

5fill in blank

hard

Fill all three blanks to write a test using the context manager fixture and assert the resource value.

PyTest

def test_resource_value([1]):
    with [2] as res:
        assert res == [3]

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

Aresource

C'resource'

D'value'

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong fixture name.

Not using 'with' statement properly.

Asserting incorrect value.

The test uses the fixture 'resource', enters its context with 'with resource as res', and asserts the value is 'resource'.

Practice

1. What is the main purpose of using a context manager fixture in pytest?

easy

A. To speed up test execution by skipping setup

B. To automatically handle setup and cleanup around a test

C. To replace assertions with print statements

D. To run tests in parallel automatically

Solution

1. Step 1: Understand context manager role

   Context managers in pytest use yield to run setup code before the test and cleanup code after the test finishes.

2. Step 2: Identify purpose in testing

   This automatic setup and cleanup makes tests safer and cleaner by managing resources like files or connections.

3. Final Answer:

   To automatically handle setup and cleanup around a test -> Option B

4. Quick Check:

   Context manager fixture = automatic setup and cleanup [OK]

Hint: Context managers wrap setup and cleanup automatically [OK]

Common Mistakes:

• Thinking context managers speed up tests by skipping setup
• Confusing context managers with parallel test execution
• Using print statements instead of assertions

2. Which of the following is the correct way to define a context manager fixture in pytest?

easy

A. @pytest.fixture
def resource():
setup()
yield
cleanup()

B. @pytest.fixture
def resource():
yield
setup()
cleanup()

C. @pytest.fixture
def resource():
setup()
cleanup()
yield

D. @pytest.fixture
def resource():
cleanup()
yield
setup()

Solution

1. Step 1: Recall context manager fixture syntax

   In pytest, the code before yield runs as setup, and the code after yield runs as cleanup.

2. Step 2: Check each option

   @pytest.fixture def resource(): setup() yield cleanup() correctly places setup() before yield and cleanup() after. Others have wrong order.

3. Final Answer:

   @pytest.fixture def resource(): setup() yield cleanup() -> Option A

4. Quick Check:

   Setup before yield, cleanup after yield [OK]

Hint: Setup code goes before yield, cleanup after yield [OK]

Common Mistakes:

• Placing cleanup before yield
• Calling setup after yield
• Putting yield at the end after cleanup

3. Given this fixture and test, what will be printed when running pytest?

@pytest.fixture
def file_resource():
    print('Setup file')
    yield
    print('Cleanup file')

def test_example(file_resource):
    print('Running test')

medium

A. Running test\nSetup file\nCleanup file

B. Cleanup file\nSetup file\nRunning test

C. Setup file\nCleanup file\nRunning test

D. Setup file\nRunning test\nCleanup file

Solution

1. Step 1: Understand fixture execution order

   Before the test runs, the fixture prints 'Setup file'. Then the test prints 'Running test'. After the test finishes, the fixture prints 'Cleanup file'.

2. Step 2: Match output sequence

   The output order is: 'Setup file', 'Running test', 'Cleanup file'.

3. Final Answer:

   Setup file\nRunning test\nCleanup file -> Option D

4. Quick Check:

   Setup -> Test -> Cleanup order [OK]

Hint: Fixture setup prints before test, cleanup prints after [OK]

Common Mistakes:

• Assuming cleanup runs before test
• Thinking test runs before setup
• Mixing order of prints

4. What is wrong with this context manager fixture?

@pytest.fixture
def db_connection():
    conn = connect_db()
    yield conn
    conn.close()

medium

A. Nothing is wrong; it is correct

B. The fixture should not yield a value

C. The cleanup code after yield will never run

D. The connection should be closed before yield

Solution

1. Step 1: Analyze fixture structure

   The fixture creates a connection, yields it for the test, then closes it after the test finishes.

2. Step 2: Confirm cleanup runs after yield

   Code after yield runs as cleanup, so conn.close() will run properly after the test.

3. Final Answer:

   Nothing is wrong; it is correct -> Option A

4. Quick Check:

   Yield passes resource, cleanup runs after yield [OK]

Hint: Cleanup code after yield always runs after test [OK]

Common Mistakes:

• Thinking cleanup code never runs
• Closing connection before yield
• Not yielding the resource

5. You want to write a context manager fixture that creates a temporary file, yields its path, and deletes the file after the test. Which code correctly implements this?

hard

A. @pytest.fixture
def temp_file():
path = '/tmp/testfile.txt'
os.remove(path)
yield path

B. @pytest.fixture
def temp_file():
path = '/tmp/testfile.txt'
yield path
open(path, 'w').close()
os.remove(path)

C. @pytest.fixture
def temp_file():
path = '/tmp/testfile.txt'
open(path, 'w').close()
yield path
os.remove(path)

D. @pytest.fixture
def temp_file():
path = '/tmp/testfile.txt'
os.remove(path)
yield
open(path, 'w').close()

Solution

1. Step 1: Setup temporary file before yield

   The file must be created before yielding its path so the test can use it.

2. Step 2: Cleanup file after yield

   After the test, the file should be deleted to clean up resources.

3. Final Answer:

   @pytest.fixture def temp_file(): path = '/tmp/testfile.txt' open(path, 'w').close() yield path os.remove(path) -> Option C

4. Quick Check:

   Create file before yield, delete after yield [OK]

Hint: Create resource before yield, clean up after yield [OK]

Common Mistakes:

• Deleting file before test runs
• Creating file after yield
• Not yielding the file path