Mock and MagicMock in PyTest - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of MagicMock call count

What is the output of the following pytest code snippet?

PyTest

from unittest.mock import MagicMock

def test_func():
    mock_obj = MagicMock()
    mock_obj.method()
    mock_obj.method()
    return mock_obj.method.call_count

result = test_func()
print(result)

A 2

B 1

C 0

D Raises AttributeError

💡 Hint

MagicMock tracks how many times a mocked method is called.

The MagicMock object tracks calls to its methods. Calling mock_obj.method() twice increments call_count to 2.

❓ assertion

intermediate

Correct assertion for mock call arguments

Which assertion correctly verifies that a MagicMock method was called with arguments (5, 10)?

PyTest

from unittest.mock import MagicMock
mock_obj = MagicMock()
mock_obj.method(5, 10)

A assert mock_obj.method.assert_called_with(5, 10)

B assert mock_obj.method.called_with(5, 10)

C assert mock_obj.method.call_args == (5, 10)

D assert mock_obj.method.call_args_list == [(5, 10)]

💡 Hint

Use the built-in MagicMock method to check call arguments.

assert_called_with is the correct method to assert the last call had specific arguments. called_with does not exist. call_args is a tuple with args and kwargs, so direct comparison to (5, 10) fails. call_args_list contains call objects, not tuples.

🔧 Debug

advanced

Identify the error in mocking a class method

What error will this pytest code raise when run?

PyTest

from unittest.mock import MagicMock

class MyClass:
    def greet(self):
        return 'Hello'

mock_instance = MagicMock(spec=MyClass)
mock_instance.greet.return_value = 'Hi'
print(mock_instance.greet())
print(mock_instance.nonexistent())

A NameError: name 'nonexistent' is not defined

B TypeError: 'MagicMock' object is not callable

C No error, prints 'Hi' and then another MagicMock object

D AttributeError: 'MagicMock' object has no attribute 'nonexistent'

💡 Hint

Spec limits attributes to those on the original class.

Using spec=MyClass restricts MagicMock to only attributes of MyClass. Calling mock_instance.nonexistent() raises AttributeError because 'nonexistent' is not defined in MyClass.

🧠 Conceptual

advanced

Purpose of using spec in MagicMock

Why is it useful to pass the 'spec' argument when creating a MagicMock object?

A It makes the mock object behave exactly like the original object including internal state

B It automatically records all calls and arguments without needing extra setup

C It restricts the mock to only allow attributes and methods that exist on the original object

D It converts the mock into a real instance of the original class

💡 Hint

Think about how spec helps catch mistakes in tests.

Passing spec limits the mock to only have attributes and methods of the original object, preventing typos and incorrect usage in tests.

❓ framework

expert

Mock patching order and effect in pytest

Given the following pytest test with patch decorators, what will be the output printed?

PyTest

from unittest.mock import patch

def get_data():
    return 'real data'

def process():
    return get_data()

@patch('__main__.get_data', return_value='mocked data 1')
@patch('__main__.get_data', return_value='mocked data 2')
def test_process(mock2, mock1):
    print(process())

test_process()

A Raises RuntimeError due to patch conflict

B mocked data 1

C real data

D mocked data 2

💡 Hint

Remember the order of patch decorators and which mock is applied last.

The outer patch decorator is applied last and overrides the inner one. The first argument mock2 corresponds to the inner patch, and mock1 to the outer patch, which returns 'mocked data 1'. So process() returns 'mocked data 1'.