Test fixtures with pytest in Flask - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the pytest module.

Flask

import [1]

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

Aflask

Bunittest

Cpytest

Drequests

Attempts:

3 left

💡 Hint

Common Mistakes

Importing flask instead of pytest

Using unittest which is a different testing framework

We import pytest to use its testing features including fixtures.

2fill in blank

medium

Complete the code to define a pytest fixture that creates a Flask app instance.

Flask

@pytest.fixture
def app():
    app = Flask(__name__)
    app.config['TESTING'] = [1]
    return app

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

AFalse

BTrue

CNone

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Setting TESTING to False disables testing features

Using None or 0 instead of True

Setting TESTING to True enables testing mode in Flask.

3fill in blank

hard

Fix the error in the test function to use the fixture correctly.

Flask

def test_home([1]):
    response = app.test_client().get('/')
    assert response.status_code == 200

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

Aapp

Brequest

Cfixture

Dclient

Attempts:

3 left

💡 Hint

Common Mistakes

Using a parameter name that does not match the fixture

Not passing any parameter to the test function

The fixture named app must be passed as a parameter to the test function.

4fill in blank

hard

Fill both blanks to create a fixture that provides a test client from the Flask app fixture.

Flask

@pytest.fixture
def client([1]):
    return [2].test_client()

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

Aapp

Bclient

Crequest

Dflask_app

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong fixture name as parameter

Returning something other than the test client

The client fixture depends on the app fixture and returns its test client.

5fill in blank

hard

Fill all three blanks to write a test using the client fixture to check the home page response.

Flask

def test_home_page([1]):
    response = [2].get('/')
    assert response.[3] == 200

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

Aclient

Cstatus_code

Dapp

Attempts:

3 left

💡 Hint

Common Mistakes

Using app instead of client in the test function

Checking a wrong attribute instead of status_code

The test function uses the client fixture to send a GET request and checks the status_code.

Practice

1. What is the main purpose of a fixture in pytest when testing a Flask app?

easy

A. To write the main application logic

B. To handle user input in the Flask app

C. To set up and tear down resources needed for tests automatically

D. To deploy the Flask app to a server

Solution

1. Step 1: Understand what fixtures do in pytest

   Fixtures prepare the environment for tests by setting up resources before tests run and cleaning them after.

2. Step 2: Identify the role of fixtures in Flask testing

   Fixtures help create test clients, databases, or other resources needed for Flask tests automatically.

3. Final Answer:

   To set up and tear down resources needed for tests automatically -> Option C

4. Quick Check:

   Fixtures = setup and cleanup [OK]

Hint: Fixtures prepare test resources automatically [OK]

Common Mistakes:

• Confusing fixtures with application code
• Thinking fixtures handle user input
• Assuming fixtures deploy the app

2. Which of the following is the correct way to define a pytest fixture for a Flask test client?

easy

A. @pytest.fixture
def client():
app = Flask(__name__)
yield app.test_client()

B. @pytest.fixture
def client():
app = Flask(__name__)
app.test_client()

C. def client():
app = Flask(__name__)
yield app.test_client()

D. @pytest.fixture
def client():
app = Flask(__name__)
return app

Solution

1. Step 1: Check the use of @pytest.fixture decorator

   The @pytest.fixture decorator is required to mark a fixture. One option lacks it.

2. Step 2: Identify correct use of yield for setup and teardown

   @pytest.fixture def client(): app = Flask(__name__) yield app.test_client() uses yield to provide the test client and allows cleanup after tests, which is best practice.

3. Final Answer:

   @pytest.fixture\ndef client():\n app = Flask(__name__)\n yield app.test_client() -> Option A

4. Quick Check:

   Use @pytest.fixture and yield for fixtures [OK]

Hint: Use @pytest.fixture and yield to define fixtures [OK]

Common Mistakes:

• Omitting @pytest.fixture decorator
• Returning instead of yielding
• Not yielding or returning the test client

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

@pytest.fixture
def sample():
    print('Setup')
    yield 'data'
    print('Teardown')

def test_example(sample):
    print(f'Test received: {sample}')

medium

A. Setup\nTest received: data\nTeardown

B. Test received: data\nSetup\nTeardown

C. Setup\nTeardown\nTest received: data

D. Test received: data

Solution

1. Step 1: Understand fixture execution order

   Before the test runs, the fixture prints 'Setup', then yields 'data' to the test.

2. Step 2: Analyze test function output and fixture teardown

   The test prints 'Test received: data'. After test finishes, fixture resumes and prints 'Teardown'.

3. Final Answer:

   Setup\nTest received: data\nTeardown -> Option A

4. Quick Check:

   Fixture setup -> test -> fixture teardown [OK]

Hint: Fixture prints before yield, teardown prints after [OK]

Common Mistakes:

• Assuming teardown runs before test
• Ignoring yield pauses fixture
• Thinking test runs before setup

4. Identify the error in this pytest fixture code for a Flask app:

@pytest.fixture
def client():
    app = Flask(__name__)
    client = app.test_client()
    return client
    print('Cleanup done')

medium

A. Fixture must use 'yield' instead of 'return' always

B. Missing '@pytest.fixture' decorator

C. 'app.test_client()' is not a valid method

D. The 'print' statement after 'return' will never execute

Solution

1. Step 1: Check code after return statement

   Code after 'return' is unreachable, so 'print' will never run.

2. Step 2: Confirm other parts are correct

   The decorator is present, 'app.test_client()' is valid, and 'return' is allowed but limits cleanup.

3. Final Answer:

   The 'print' statement after 'return' will never execute -> Option D

4. Quick Check:

   Code after return is unreachable [OK]

Hint: Code after return is ignored; use yield for cleanup [OK]

Common Mistakes:

• Thinking print runs after return
• Assuming return disallows fixture
• Confusing method names

5. You want to create a fixture that sets up a temporary database for Flask tests and ensures it is cleaned up after all tests in the module run. Which fixture scope and structure is best?

hard

A. @pytest.fixture(scope='function')
def temp_db():
db = setup_temp_db()
yield db
teardown_temp_db(db)

B. @pytest.fixture(scope='module')
def temp_db():
db = setup_temp_db()
yield db
teardown_temp_db(db)

C. @pytest.fixture(scope='session')
def temp_db():
db = setup_temp_db()
return db

D. @pytest.fixture(scope='module')
def temp_db():
db = setup_temp_db()
return db
teardown_temp_db(db)

Solution

1. Step 1: Choose fixture scope for module-wide setup

   Scope 'module' runs once per module, ideal for shared DB setup across tests.

2. Step 2: Use yield to allow teardown after all tests

   Yield pauses fixture to run tests, then runs teardown after all tests complete.

3. Final Answer:

   @pytest.fixture(scope='module')\ndef temp_db():\n db = setup_temp_db()\n yield db\n teardown_temp_db(db) -> Option B

4. Quick Check:

   Module scope + yield for setup and cleanup [OK]

Hint: Use scope='module' and yield for setup/cleanup [OK]

Common Mistakes:

• Using function scope causes repeated setup
• Returning without yield skips cleanup
• Placing cleanup code after return