{"id":3655,"date":"2022-07-04T09:20:57","date_gmt":"2022-07-04T09:20:57","guid":{"rendered":"https:\/\/www.pythontutorial.net\/?page_id=3655"},"modified":"2022-07-09T07:41:41","modified_gmt":"2022-07-09T07:41:41","slug":"python-unittest-mock","status":"publish","type":"page","link":"https:\/\/www.pythontutorial.net\/python-unit-testing\/python-unittest-mock\/","title":{"rendered":"Python Unittest Mock"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you’ll learn about the Python unittest<\/a> Mock class and how to use it to mock other classes.<\/p>\n\n\n\n

Introduction to Python unittest Mock class #<\/a><\/h2>\n\n\n\n

Mocks simulate the behaviors of real objects. To test an object that depends on other objects in an isolated manner, you use mock objects to mock the real objects.<\/p>\n\n\n\n

To mock objects, you use the unittest.mock<\/code> module. The unittest.mock<\/code> module provides the Mock<\/code> class that allows you to mock other objects.<\/p>\n\n\n\n

It also provides the MagicMock<\/code> class that is a subclass of the Mock<\/code> class. Besides the methods and properties of the Mock<\/code> class, the MagicMock<\/code> class has the implementations of all the dunder methods e.g., __str__<\/a> and __repr__<\/a>.<\/p>\n\n\n\n

See the following example:<\/p>\n\n\n

from<\/span> unittest.mock import<\/span> Mock\n\n\n# create a new mock object<\/span>\nmock = Mock()\n\n# mock the api function<\/span>\nmock.api.return_value = {\n    'id'<\/span>: 1<\/span>,\n    'message'<\/span>: 'hello'<\/span>\n}\n# call the api function<\/span>\nprint(mock.api())<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
{'id'<\/span>: 1<\/span>, 'message'<\/span>: 'hello'<\/span>}<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
How it works.<\/p>\n\n\n\n
First, import the Mock<\/code> class from the unittest.mock<\/code> module:<\/p>\n\n\n
from<\/span> unittest.mock import<\/span> Mock<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Second, create a new instance of the Mock<\/code> class:<\/p>\n\n\n
mock = Mock()<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Third, mock the api()<\/code> function and assign its return value to a dictionary:<\/p>\n\n\n
mock.api.return_value = {\n    'id'<\/span>: 1<\/span>,\n    'message'<\/span>: 'hello'<\/span>\n}<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Finally, call the api()<\/code> from the mock object. It’ll return the assigned value:<\/p>\n\n\n
print(mock.api())<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
In this example, we have two mock objects: mock<\/code> & mock.api<\/code>.<\/p>\n\n\n\n
Let’s add the print()<\/code> statement to the program to see how it works:<\/p>\n\n\n
from<\/span> unittest.mock import<\/span> Mock\n\n\n# create a new mock object<\/span>\nmock = Mock()\nprint(mock)\n\n# mock the api function<\/span>\nmock.api.return_value = {\n    'id'<\/span>: 1<\/span>,\n    'message'<\/span>: 'hello'<\/span>\n}\nprint(mock.api)\n\n# call the api<\/span>\nprint(mock.api())<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
<Mock id='1830094470496'<\/span>>\n<Mock name='mock.api'<\/span> id='1830100086416'<\/span>>\n{'id'<\/span>: 1<\/span>, 'message'<\/span>: 'hello'<\/span>}<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
The output shows two Mock<\/code> objects.<\/p>\n\n\n\n
In short, if you assign a property that doesn’t exist on the Mock<\/code> object, Python will return a new mock object. Because of this dynamic, you can use the Mock<\/code> class to mock any objects that you want.<\/p>\n\n\n\n
When to use mock #<\/a><\/h2>\n\n\n\n
These are cases that you may consider using mocks:<\/p>\n\n\n\n