{"id":3589,"date":"2022-07-01T06:30:21","date_gmt":"2022-07-01T06:30:21","guid":{"rendered":"https:\/\/www.pythontutorial.net\/?page_id=3589"},"modified":"2022-07-09T07:40:07","modified_gmt":"2022-07-09T07:40:07","slug":"python-asserttrue","status":"publish","type":"page","link":"https:\/\/www.pythontutorial.net\/python-unit-testing\/python-asserttrue\/","title":{"rendered":"Python assertTrue()"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you’ll learn how to use Python assertTrue()<\/code> to test if an expression is True and assertFalse()<\/code> method to test if an expression is False.<\/p>\n\n\n\n

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

The assertTrue()<\/code><\/code> is a method of the TestCase<\/code> class in the unittest<\/a> module. The assertTrue()<\/code><\/code> method tests if an expression is True<\/code>:<\/p>\n\n\n

assertTrue(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 True<\/code>, the test passes. Otherwise, the test fails. <\/p>\n\n\n\n
The msg<\/code> is optional. If you pass the msg<\/code> parameter, it’ll be displayed when the test fails.<\/p>\n\n\n\n
The assertTrue()<\/code> method is equivalent to the following expression:<\/p>\n\n\n
bool(expr) is<\/span> True<\/span><\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
It is not equivalent to the following:<\/p>\n\n\n
expr is<\/span> True<\/span><\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
In practice, you should use the assertTrue()<\/code><\/code><\/code> method to test the boolean of a variable. Also, you should not use the assertTrue()<\/code><\/code><\/code> method if more specific methods are available. <\/p>\n\n\n\n
For example, instead of using the assertTrue()<\/code><\/code><\/code> method for the following case:<\/p>\n\n\n
assertTrue(a == b)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
you should use the assertEqual()<\/code> method instead:<\/p>\n\n\n
assertEqual(a,b)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Because the assertEqual()<\/code> method provides a more clear error message in case the test fails.<\/p>\n\n\n\n
Python assertTrue() method example #<\/a><\/h2>\n\n\n\n
The following example uses the assertTrue()<\/code> method to test if all characters in a string are digits:<\/p>\n\n\n
import<\/span> unittest\n\n\nclass<\/span> TestBool<\/span>(unittest.TestCase)<\/span>:<\/span>\n    def<\/span> test_is_digit<\/span>(self)<\/span>:<\/span>\n        str = '123'<\/span>\n        self.assertTrue(str.isdigit())<\/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_is_digit (test_bool.TestBool) ... ok\n\n----------------------------------------------------------------------\nRan 1<\/span> test in<\/span> 0.000<\/span>s\n\nOK<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Python assertFalse() method #<\/a><\/h2>\n\n\n\n
The assertFalse()<\/code> method tests if an expression is False<\/code>. For example:<\/p>\n\n\n
import<\/span> unittest\n\n\nclass<\/span> TestBool<\/span>(unittest.TestCase)<\/span>:<\/span>\n    def<\/span> test_empty_string_is_digit<\/span>(self)<\/span>:<\/span>\n        str = ''<\/span>\n        self.assertFalse(str.isdigit())\n\n    def<\/span> test_alpha_is_digit<\/span>(self)<\/span>:<\/span>\n        str = 'a00'<\/span>\n        self.assertFalse(str.isdigit())<\/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_alpha_is_digit (test_bool.TestBool) ... ok\ntest_empty_string_is_digit (test_bool.TestBool) ... ok\ntest_is_digit (test_bool.TestBool) ... ok\n\n----------------------------------------------------------------------\nRan 3<\/span> tests in<\/span> 0.001<\/span>s\n\nOK<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Summary #<\/a><\/h2>\n\n\n\n
  • Use the assertTrue()<\/code> method to test if an expression is True<\/li>
  • Use the assertFalse()<\/code> method to test if an expression is False<\/li><\/ul>\n
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