Mock return values and side effects in PyTest - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set a mock's return value.

PyTest

from unittest.mock import Mock
mock_obj = Mock()
mock_obj.method.return_value = [1]
assert mock_obj.method() == 10

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

A10

B'10'

CNone

DFalse

Attempts:

3 left

💡 Hint

Common Mistakes

Using a string '10' instead of integer 10

Setting return_value to None

The return_value sets what the mock method returns. Here, it should be the integer 10, not a string.

2fill in blank

medium

Complete the code to set a mock's side effect to raise an exception.

PyTest

from unittest.mock import Mock
mock_obj = Mock()
mock_obj.method.side_effect = [1]
try:
    mock_obj.method()
except ValueError:
    caught = True
else:
    caught = False
assert caught is True

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

AException('error')

BRuntimeError('error')

CValueError('error')

DTypeError('error')

Attempts:

3 left

💡 Hint

Common Mistakes

Using Exception instead of ValueError

Using a different exception type

The side_effect can be set to an exception instance to make the mock raise it when called. The test expects a ValueError.

3fill in blank

hard

Fix the error in setting a mock's side effect to return different values on each call.

PyTest

from unittest.mock import Mock
mock_obj = Mock()
mock_obj.method.side_effect = [1]
assert mock_obj.method() == 1
assert mock_obj.method() == 2
assert mock_obj.method() == 3

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

A1, 2, 3

B(1, 2, 3)

C{1, 2, 3}

D[1, 2, 3]

Attempts:

3 left

💡 Hint

Common Mistakes

Using a set which is unordered

Using a tuple which works but list is preferred for mutability

The side_effect can be set to a list to return each value on successive calls. A list preserves order and allows repeated calls.

4fill in blank

hard

Fill both blanks to create a mock that returns 5 and then raises an exception on the second call.

PyTest

from unittest.mock import Mock
mock_obj = Mock()
mock_obj.method.side_effect = [[1], [2]]
assert mock_obj.method() == 5
try:
    mock_obj.method()
except ValueError:
    caught = True
else:
    caught = False
assert caught is True

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A5

BValueError('fail')

CValueError

DException('fail')

Attempts:

3 left

💡 Hint

Common Mistakes

Using exception type instead of instance in side_effect list

Mismatch between exception raised and caught

The side_effect list must have the return value 5 first, then the exception instance. The except block catches the exception type, which is ValueError.

5fill in blank

hard

Fill all three blanks to create a mock that returns the length of input string, then raises TypeError, then returns 'done'.

PyTest

from unittest.mock import Mock
mock_obj = Mock()
mock_obj.method.side_effect = [lambda s: len(s), [1], [2]]
assert mock_obj.method('test') == 4
try:
    mock_obj.method('fail')
except [3]:
    caught = True
else:
    caught = False
assert caught is True
assert mock_obj.method('end') == 'done'

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

ATypeError('wrong type')

BValueError('error')

Cdone

DTypeError

Attempts:

3 left

💡 Hint

Common Mistakes

Using exception type instead of instance in side_effect list

Mismatch between exception raised and caught

The side_effect list has a lambda returning length, then a TypeError instance, then a string 'done'. The except block catches TypeError type.