{"id":3582,"date":"2022-07-01T04:28:10","date_gmt":"2022-07-01T04:28:10","guid":{"rendered":"https:\/\/www.pythontutorial.net\/?page_id=3582"},"modified":"2022-07-09T07:36:39","modified_gmt":"2022-07-09T07:36:39","slug":"python-assertis","status":"publish","type":"page","link":"https:\/\/www.pythontutorial.net\/python-unit-testing\/python-assertis\/","title":{"rendered":"Python assertIs()"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you’ll learn how to use the Python assertIs()<\/code> to test if two objects are the same.<\/p>\n\n\n\n

Introduction to Python assertIs() method #<\/a><\/h2>\n\n\n\n

The assertIs()<\/code><\/code> allows you to test if two objects are the same. The following shows the syntax of the assertIs()<\/code><\/code> method:<\/p>\n\n\n

assertIs(first, second, msg=None<\/span>)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
If the first<\/code> and second<\/code> reference the same object, the test will pass. Otherwise, it’ll fail. <\/p>\n\n\n\n
The msg<\/code> is optional. It’s displayed in the test result in case the test fails.<\/p>\n\n\n\n
Technically, the assertIs()<\/code> method uses the is<\/code> operator:<\/p>\n\n\n
first is second<\/code><\/span><\/pre>\n\n\n
Python assertIs() method example #<\/a><\/h2>\n\n\n\n
First, create a Logger<\/code> singleton class in the logger.py<\/code> module:<\/p>\n\n\n
from<\/span> datetime import<\/span> datetime\n\n\nclass<\/span> Logger<\/span>:<\/span>\n    _instance = None<\/span>\n\n    def<\/span> __new__<\/span>(cls)<\/span>:<\/span>\n        if<\/span> cls._instance is<\/span> None<\/span>:\n            cls._instance = super(Logger, cls).__new__(cls)\n        return<\/span> cls._instance\n\n    def<\/span> log<\/span>(self, message)<\/span>:<\/span>\n        print(f'{datetime.now().strftime(\"%Y-%m-%d %H:%M:%S\"<\/span>)}<\/span> {message}<\/span>'<\/span>)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
The singleton is a design pattern that limits the instantiation of a class to a single instance. In other words, you’ll have the same Logger<\/code> object regardless of how many times you call the Logger()<\/code> constructor.<\/p>\n\n\n\n
Second, create a TestLogger<\/code> class that tests the Logger<\/code> class:<\/p>\n\n\n
import<\/span> unittest\n\nfrom<\/span> logger import<\/span> Logger\n\n\nclass<\/span> TestLogger<\/span>(unittest.TestCase)<\/span>:<\/span>\n    def<\/span> setUp<\/span>(self)<\/span>:<\/span>\n        self.logger = Logger()\n\n    def<\/span> test_singleton<\/span>(self)<\/span>:<\/span>\n        new_logger = Logger()\n        self.assertIs(self.logger, new_logger)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
In the TestLogger<\/code> class:<\/p>\n\n\n\n