{"id":3594,"date":"2022-07-02T02:02:43","date_gmt":"2022-07-02T02:02:43","guid":{"rendered":"https:\/\/www.pythontutorial.net\/?page_id=3594"},"modified":"2022-07-09T07:38:26","modified_gmt":"2022-07-09T07:38:26","slug":"python-assertisnone","status":"publish","type":"page","link":"https:\/\/www.pythontutorial.net\/python-unit-testing\/python-assertisnone\/","title":{"rendered":"Python assertIsNone()"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you’ll learn how to use the Python assertIsNone()<\/code> method to test if an expression is None<\/code>.<\/p>\n\n\n\n

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

The assertIsNone()<\/code><\/code> is a method of the TestCase<\/code> class of the unittest<\/a> module. The assertIsNone()<\/code><\/code> test if an expression is None<\/a>:<\/p>\n\n\n

assertIsNone(expr, msg=None<\/span>)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
If the expr<\/code> is None<\/code>, the test passes. Otherwise, the test will fail.<\/p>\n\n\n\n
The msg<\/code> is optional. It’ll be displayed in the test result if the test fails.<\/p>\n\n\n\n
Python assertIsNone() method examples #<\/a><\/h2>\n\n\n\n
Let’s take some examples of using the assertIsNone()<\/code> method.<\/p>\n\n\n\n
1) Using assertIsNone() with a success case #<\/a><\/h3>\n\n\n\n
The following example uses the assertIsNone()<\/code> to test if the message variable is None:<\/p>\n\n\n
import<\/span> unittest\n\n\nclass<\/span> TestNone<\/span>(unittest.TestCase)<\/span>:<\/span>\n    def<\/span> test_variable_none<\/span>(self)<\/span>:<\/span>\n        message = None<\/span>\n        self.assertIsNone(message)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Run the test:<\/p>\n\n\n
python -m unittest -v<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
test_variable_none (test_none.TestNone) ... ok\n\n----------------------------------------------------------------------\nRan 1 test in 0.000s<\/code><\/span>Code language:<\/span> plaintext<\/span> (<\/span>plaintext<\/span>)<\/span><\/small><\/pre>\n\n\n
2) Using assertIsNone() with a failed case #<\/a><\/h3>\n\n\n\n
The following example uses the assertIsNone()<\/code> method to test if the message<\/code> variable is None:<\/p>\n\n\n
import<\/span> unittest\n\n\nclass<\/span> TestNone<\/span>(unittest.TestCase)<\/span>:<\/span>\n    def<\/span> test_variable_not_none<\/span>(self)<\/span>:<\/span>\n        message = 'Hello'<\/span>\n        self.assertIsNone(message)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Run the test:<\/p>\n\n\n
python -m unittest -v<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
test_variable_not_none (test_none.TestNone) ... FAIL\n\n======================================================================\nFAIL: test_variable_not_none (test_none.TestNone)\n----------------------------------------------------------------------\nTraceback (most recent call last):\n  File \"D:\\python-unit-testing\\test_none.py\", line 7, in test_variable_not_none\n    self.assertIsNone(message)\nAssertionError: 'Hello' is not None\n\n----------------------------------------------------------------------\nRan 1 test in 0.001s\n\nFAILED (failures=1)<\/code><\/span>Code language:<\/span> plaintext<\/span> (<\/span>plaintext<\/span>)<\/span><\/small><\/pre>\n\n\n
Since the message is 'Hello'<\/code>, it is not None. Therefore, the test failed.<\/p>\n\n\n\n
3) Using assertIsNone() with a failed case with a message #<\/a><\/h3>\n\n\n\n
The following example uses the assertIsNone()<\/code> to test if the message variable is None. Also, we show a message when the test fails:<\/p>\n\n\n
import<\/span> unittest\n\n\nclass<\/span> TestNone<\/span>(unittest.TestCase)<\/span>:<\/span>\n    def<\/span> test_variable_not_none<\/span>(self)<\/span>:<\/span>\n        message = 'Hello'<\/span>\n        self.assertIsNone(\n            message,\n            f'The message is \"{message}<\/span>\" so it is not None.'<\/span>\n        )<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Run the test:<\/p>\n\n\n
python -m unittest -v<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
test_variable_not_none (test_none.TestNone) ... FAIL\n\n======================================================================\nFAIL: test_variable_not_none (test_none.TestNone)\n----------------------------------------------------------------------\nTraceback (most recent call last):\n  File \"D:\\python-unit-testing\\test_none.py\", line 7, in test_variable_not_none\n    self.assertIsNone(\nAssertionError: 'Hello' is not None : The message is \"Hello\" so it is not None.\n\n----------------------------------------------------------------------\nRan 1 test in 0.001s\n\nFAILED (failures=1)<\/code><\/span>Code language:<\/span> plaintext<\/span> (<\/span>plaintext<\/span>)<\/span><\/small><\/pre>\n\n\n
Python assertIsNotNone() method #<\/a><\/h2>\n\n\n\n
The assertIsNotNone()<\/code><\/code> is opposite of the assertIsNone()<\/code> method. The assertIsNotNone()<\/code><\/code> method tests if a variable is not None.<\/p>\n\n\n
assertIsNotNone(expr, msg=None<\/span>)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
The test passes if the expr<\/code> is not None<\/code> or fails otherwise. For example:<\/p>\n\n\n
import<\/span> unittest\n\n\nclass<\/span> TestNone<\/span>(unittest.TestCase)<\/span>:<\/span>\n    def<\/span> test_variable_is_not_none<\/span>(self)<\/span>:<\/span>\n        message = 'Bye'<\/span>\n        self.assertIsNotNone(message)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Run the test:<\/p>\n\n\n
python -m unittest -v<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
test_variable_is_not_none (test_not_none.TestNone) ... ok\n\n----------------------------------------------------------------------\nRan 1 test in 0.001s\n\nOK<\/code><\/span>Code language:<\/span> plaintext<\/span> (<\/span>plaintext<\/span>)<\/span><\/small><\/pre>\n\n\n
Summary #<\/a><\/h2>\n\n\n\n
  • Use the assertIsNone()<\/code> method to test if a variable is None<\/code>.<\/li>
  • use the assertIsNotNone()<\/code> method to test if a variable is not None<\/code>.<\/li><\/ul>\n
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