monkeypatch.setattr in PyTest - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to replace the function using monkeypatch.setattr.

PyTest

def test_func(monkeypatch):
    def fake_return():
        return 42
    monkeypatch.setattr('module.func', [1])
    assert module.func() == 42

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

Afunc

Bmodule.func

Creturn 42

Dfake_return

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the function name as a string instead of the function object.

Using the original function instead of the fake function.

We use monkeypatch.setattr to replace 'module.func' with the fake_return function.

2fill in blank

medium

Complete the code to patch the attribute 'value' of the object using monkeypatch.setattr.

PyTest

class MyClass:
    value = 10

def test_value(monkeypatch):
    obj = MyClass()
    monkeypatch.setattr(obj, 'value', [1])
    assert obj.value == 99

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

A99

B10

C'value'

Dobj.value

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the old value 10 instead of the new value.

Passing the attribute name instead of the new value.

We patch the attribute 'value' to be 99, so obj.value should equal 99.

3fill in blank

hard

Fix the error in the code to correctly patch the function using monkeypatch.setattr.

PyTest

def original():
    return 'original'

def fake():
    return 'fake'

def test_patch(monkeypatch):
    monkeypatch.setattr("original", [1])
    assert original() == 'fake'

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

A'fake'

Bfake

C'original'

Doriginal

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the function name as a string.

Passing the original function instead of the fake function.

monkeypatch.setattr expects the target and the new value (function) to replace it. We pass the function fake without quotes.

4fill in blank

hard

Fill both blanks to patch the method 'get_data' of the class 'DataClass' to return 'mocked'.

PyTest

class DataClass:
    def get_data(self):
        return 'real'

def test_data(monkeypatch):
    monkeypatch.setattr(DataClass, [1], [2])
    obj = DataClass()
    assert obj.get_data() == 'mocked'

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

A'get_data'

Blambda self: 'mocked'

C'getData'

Dlambda: 'mocked'

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong method name string.

Using lambda without self parameter.

We patch the method 'get_data' with a lambda that takes self and returns 'mocked'.

5fill in blank

hard

Fill all three blanks to patch the function 'calculate' in module 'calc' to return 100 during the test.

PyTest

import calc

def fake_calc():
    return 100

def test_calculate(monkeypatch):
    monkeypatch.setattr(calc, [1], [2])
    result = calc.calculate()
    assert result == [3]

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

A'calculate'

Bfake_calc

C100

D'calc'

Attempts:

3 left

💡 Hint

Common Mistakes

Passing function name without quotes.

Passing the function name as string instead of function object.

Asserting wrong expected value.

We patch 'calculate' in calc module with fake_calc function and assert the result is 100.

Practice

1. What is the main purpose of monkeypatch.setattr in pytest?

easy

A. To temporarily replace an attribute or function during a test

B. To permanently change code in the source files

C. To skip a test function

D. To run tests in parallel

Solution

1. Step 1: Understand monkeypatch.setattr usage

   It is used to temporarily replace or modify attributes or functions during a test to isolate behavior.

2. Step 2: Differentiate from other pytest features

   It does not permanently change code or skip tests; it only affects the test scope temporarily.

3. Final Answer:

   To temporarily replace an attribute or function during a test -> Option A

4. Quick Check:

   Temporary replacement = A [OK]

Hint: Think 'temporary change' during test only [OK]

Common Mistakes:

• Confusing temporary patching with permanent code changes
• Thinking it skips tests
• Assuming it runs tests in parallel

2. Which of the following is the correct syntax to patch the function get_data in module my_module using monkeypatch in pytest?

easy

A. monkeypatch.setattr('get_data', my_module, lambda: 42)

B. monkeypatch.setattr('my_module.get_data', lambda: 42)

C. monkeypatch.setattr(my_module, 'get_data', lambda: 42)

D. monkeypatch.setattr('my_module', 'get_data', 42)

Solution

1. Step 1: Identify correct monkeypatch.setattr signature

   The correct usage is monkeypatch.setattr(target_object, attribute_name, new_value).

2. Step 2: Match parameters to patch get_data function

   We pass the module object my_module, the attribute name 'get_data', and the replacement function lambda: 42.

3. Final Answer:

   monkeypatch.setattr(my_module, 'get_data', lambda: 42) -> Option C

4. Quick Check:

   Object, attribute, new value = A [OK]

Hint: Pass object, attribute name, then new value [OK]

Common Mistakes:

• Passing attribute as a string path instead of object and attribute
• Swapping parameters order
• Passing value instead of function for patching

3. Given the code below, what will be the output of the test?

import my_module

def test_func(monkeypatch):
    def fake_func():
        return 10
    monkeypatch.setattr(my_module, 'get_value', fake_func)
    result = my_module.get_value()
    print(result)

medium

A. None

B. Original value from my_module.get_value()

C. AttributeError

D. 10

Solution

1. Step 1: Understand monkeypatch effect on get_value

   The original my_module.get_value is replaced temporarily by fake_func which returns 10.

2. Step 2: Evaluate the call and print output

   Calling my_module.get_value() inside the test calls fake_func(), so it prints 10.

3. Final Answer:

   10 -> Option D

4. Quick Check:

   Patched function returns 10 [OK]

Hint: Patched function output replaces original during test [OK]

Common Mistakes:

• Expecting original function output instead of patched
• Thinking patch is permanent outside test
• Assuming print outputs None

4. What is wrong with the following pytest test using monkeypatch?

def test_example(monkeypatch):
    monkeypatch.setattr('os.path.exists', lambda x: True)
    assert os.path.exists('anyfile.txt') == True

medium

A. The lambda function should accept no arguments

B. The first argument to setattr should be the module object, not a string

C. os.path.exists cannot be patched

D. The assert statement is incorrect

Solution

1. Step 1: Check monkeypatch.setattr usage

   The first argument must be the module or object, not a string path.

2. Step 2: Identify correct usage

   It should be monkeypatch.setattr(os.path, 'exists', lambda x: True) to patch the function properly.

3. Final Answer:

   The first argument to setattr should be the module object, not a string -> Option B

4. Quick Check:

   Object, not string path = B [OK]

Hint: Pass object, not string path, as first argument [OK]

Common Mistakes:

• Passing string path instead of module object
• Incorrect lambda parameters
• Assuming some functions cannot be patched

5. You want to test a function fetch_data() that calls requests.get. How can you use monkeypatch.setattr to replace requests.get with a fake function that returns a mock response with status_code=200 and text='OK'?

hard

A. Define a fake function returning a mock object, then patch with monkeypatch.setattr(requests, 'get', fake_func)

B. Patch requests.get with a string 'mock' using monkeypatch.setattr

C. Use monkeypatch.setattr('requests.get', fake_func) with a lambda returning 200

D. Replace fetch_data with a fake function instead of patching requests.get

Solution

1. Step 1: Create a fake function returning a mock response

   Define a function that returns an object with status_code=200 and text='OK'.

2. Step 2: Patch requests.get with monkeypatch.setattr

   Use monkeypatch.setattr(requests, 'get', fake_func) to replace the real HTTP call during the test.

3. Final Answer:

   Define a fake function returning a mock object, then patch with monkeypatch.setattr(requests, 'get', fake_func) -> Option A

4. Quick Check:

   Patch requests.get with fake function = D [OK]

Hint: Patch requests.get with a fake function returning mock response [OK]

Common Mistakes:

• Passing string path instead of module object
• Patching with wrong types like strings
• Replacing the wrong function instead of requests.get