{"id":3557,"date":"2022-06-30T07:23:30","date_gmt":"2022-06-30T07:23:30","guid":{"rendered":"https:\/\/www.pythontutorial.net\/?page_id=3557"},"modified":"2022-07-03T23:52:23","modified_gmt":"2022-07-03T23:52:23","slug":"python-unittest","status":"publish","type":"page","link":"https:\/\/www.pythontutorial.net\/python-unit-testing\/python-unittest\/","title":{"rendered":"Python unittest"},"content":{"rendered":"\n<p><strong>Summary<\/strong>: in this tutorial, you&#8217;ll learn about the unit test concept and how to use the Python <code>unittest<\/code> module to perform unit testing.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id='what-is-a-unit-test'>What is a unit test <a href=\"#what-is-a-unit-test\" class=\"anchor\" id=\"what-is-a-unit-test\" title=\"Anchor for What is a unit test\">#<\/a><\/h2>\n\n\n\n<p>A unit test is an automated test that:<\/p>\n\n\n\n<ul class=\"wp-block-list\"><li>Verifies a small piece of code called a unit. A unit can be a <a href=\"https:\/\/www.pythontutorial.net\/python-basics\/python-functions\/\">function<\/a> or a method of a <a href=\"https:\/\/www.pythontutorial.net\/python-oop\/python-class\/\">class<\/a>.<\/li><li>Runs very fast.<\/li><li>Executes in an isolated manner.<\/li><\/ul>\n\n\n\n<p>The idea of unit testing is to check each small piece of your program to ensure it works properly. It&#8217;s different from integration testing which tests that different parts of the program work well together.<\/p>\n\n\n\n<p>The goal of a unit test is to find bugs. Also, a unit test can help refactor existing code to make it more testable and robust.<\/p>\n\n\n\n<p>Python provides you with a built-in module <code>unittest<\/code> that allows you to carry out unit testing effectively.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id='xunit-terminology'>xUnit terminology <a href=\"#xunit-terminology\" class=\"anchor\" id=\"xunit-terminology\" title=\"Anchor for xUnit terminology\">#<\/a><\/h2>\n\n\n\n<p>The <code>unittest<\/code> module follows the xUnit philosophy. It has the following major components:<\/p>\n\n\n\n<ul class=\"wp-block-list\"><li><strong>System under test<\/strong> is a function, a class, a method that will be tested.<\/li><li><strong>Test case class<\/strong> (<code>unittest.TestCase<\/code>): is the base class for all the test classes. In other words, all test classes are subclasses of the TestCase class in the <code>unittest<\/code> module.<\/li><li><strong><a href=\"https:\/\/www.pythontutorial.net\/python-unit-testing\/python-test-fixtures\/\">Test fixtures<\/a><\/strong> are methods that execute before and after a test method executes.<\/li><li><strong>Assertions<\/strong> are methods that check the behavior of the component being tested.<\/li><li><strong>Test suite<\/strong> is a group of related tests executed together.<\/li><li><strong>Test runner <\/strong>is a program that runs the test suite.<\/li><\/ul>\n\n\n\n<h2 class=\"wp-block-heading\" id='python-unittest-example'>Python unittest example <a href=\"#python-unittest-example\" class=\"anchor\" id=\"python-unittest-example\" title=\"Anchor for Python unittest example\">#<\/a><\/h2>\n\n\n\n<p>Suppose you have <code>Square<\/code> class that has a property called <code>length<\/code> and a method <code>area()<\/code> that returns the area of the square. The <code>Square<\/code> class is in the <code>square.py<\/code> module:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-1\" data-shcb-language-name=\"Python\" data-shcb-language-slug=\"python\"><span><code class=\"hljs language-python\"><span class=\"hljs-class\"><span class=\"hljs-keyword\">class<\/span> <span class=\"hljs-title\">Square<\/span>:<\/span>\n    <span class=\"hljs-function\"><span class=\"hljs-keyword\">def<\/span> <span class=\"hljs-title\">__init__<\/span><span class=\"hljs-params\">(self, length)<\/span> -&gt; <span class=\"hljs-keyword\">None<\/span>:<\/span>\n        self.length = length\n\n    <span class=\"hljs-function\"><span class=\"hljs-keyword\">def<\/span> <span class=\"hljs-title\">area<\/span><span class=\"hljs-params\">(self)<\/span>:<\/span>\n        <span class=\"hljs-keyword\">return<\/span> self.length * self.length<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-1\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">Python<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">python<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>To test the <code>Square<\/code> class, you create a new file called <code>test_square.py<\/code> file and import the <code>unittest<\/code> module like this:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-2\" data-shcb-language-name=\"Python\" data-shcb-language-slug=\"python\"><span><code class=\"hljs language-python\"><span class=\"hljs-keyword\">import<\/span> unittest<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-2\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">Python<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">python<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>Since the <code>test_square.py<\/code> needs to access the <code>Square<\/code> class, you have to import it from the <code>square.py<\/code> module:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-3\" data-shcb-language-name=\"Python\" data-shcb-language-slug=\"python\"><span><code class=\"hljs language-python\"><span class=\"hljs-keyword\">import<\/span> unittest\n\n<span class=\"hljs-keyword\">from<\/span> square <span class=\"hljs-keyword\">import<\/span> Square<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-3\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">Python<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">python<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>To create a test case, you define a new class called <code>TestSquare<\/code> that inherits from the <code>TestCase<\/code> class of the <code>unittest<\/code> module:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-4\" data-shcb-language-name=\"Python\" data-shcb-language-slug=\"python\"><span><code class=\"hljs language-python\"><span class=\"hljs-class\"><span class=\"hljs-keyword\">class<\/span> <span class=\"hljs-title\">TestSquare<\/span><span class=\"hljs-params\">(unittest.TestCase)<\/span>:<\/span>\n   <span class=\"hljs-keyword\">pass<\/span><\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-4\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">Python<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">python<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>To test the <code>area()<\/code> method, you add a method called <code>test_area()<\/code> to the <code>TestSquare<\/code> class like this:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-5\" data-shcb-language-name=\"Python\" data-shcb-language-slug=\"python\"><span><code class=\"hljs language-python\"><span class=\"hljs-keyword\">import<\/span> unittest\n\n<span class=\"hljs-keyword\">from<\/span> square <span class=\"hljs-keyword\">import<\/span> Square\n\n\n<span class=\"hljs-class\"><span class=\"hljs-keyword\">class<\/span> <span class=\"hljs-title\">TestSquare<\/span><span class=\"hljs-params\">(unittest.TestCase)<\/span>:<\/span>\n    <span class=\"hljs-function\"><span class=\"hljs-keyword\">def<\/span> <span class=\"hljs-title\">test_area<\/span><span class=\"hljs-params\">(self)<\/span>:<\/span>\n        square = Square(<span class=\"hljs-number\">10<\/span>)\n        area = square.area()\n        self.assertEqual(area, <span class=\"hljs-number\">100<\/span>)<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-5\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">Python<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">python<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>In the <code>test_area()<\/code> method:<\/p>\n\n\n\n<ul class=\"wp-block-list\"><li>First, create a new instance of the <code>Square<\/code> class and initialize its radius with the number 10.<\/li><li>Second, call the <code>area()<\/code> method that returns the area of the square.<\/li><li>Third, call the <code>assertEqual()<\/code> method to check if the result returned by the <code>area()<\/code> method is equal to an expected area (<code>100<\/code>).<\/li><\/ul>\n\n\n\n<p>If the area is equal to 100, the <code>assertEqual()<\/code> will pass the test. Otherwise, the <code>assertEqual()<\/code> will fail the test.<\/p>\n\n\n\n<p>Before running the test, you need to call the <code>main()<\/code> function of the <code>unittest<\/code> module as follows:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-6\" data-shcb-language-name=\"Python\" data-shcb-language-slug=\"python\"><span><code class=\"hljs language-python\"><span class=\"hljs-keyword\">import<\/span> unittest\n\n<span class=\"hljs-keyword\">from<\/span> square <span class=\"hljs-keyword\">import<\/span> Square\n\n\n<span class=\"hljs-class\"><span class=\"hljs-keyword\">class<\/span> <span class=\"hljs-title\">TestSquare<\/span><span class=\"hljs-params\">(unittest.TestCase)<\/span>:<\/span>\n    <span class=\"hljs-function\"><span class=\"hljs-keyword\">def<\/span> <span class=\"hljs-title\">test_area<\/span><span class=\"hljs-params\">(self)<\/span>:<\/span>\n        square = Square(<span class=\"hljs-number\">10<\/span>)\n        area = square.area()\n        self.assertEqual(area, <span class=\"hljs-number\">100<\/span>)\n\n\n<span class=\"hljs-keyword\">if<\/span> __name__ == <span class=\"hljs-string\">'__main__'<\/span>:\n    unittest.main()<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-6\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">Python<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">python<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>To run the test, you open the terminal, navigate to the folder, and execute the following command:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-7\" data-shcb-language-name=\"Python\" data-shcb-language-slug=\"python\"><span><code class=\"hljs language-python\">python test_square.py<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-7\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">Python<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">python<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>If you use Linux or macOS, you need to use the python3 command instead:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-8\" data-shcb-language-name=\"Python\" data-shcb-language-slug=\"python\"><span><code class=\"hljs language-python\">python3 test_square.py<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-8\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">Python<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">python<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>It&#8217;ll output the following:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-9\" data-shcb-language-name=\"plaintext\" data-shcb-language-slug=\"plaintext\"><span><code class=\"hljs language-plaintext\">.\n----------------------------------------------------------------------\nRan 1 test in 0.000s\n\nOK<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-9\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">plaintext<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">plaintext<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>The output indicates that one test has passed denoted by the dot (.)  If a test failed, you would see the letter <code>F<\/code> instead of the dot (.)<\/p>\n\n\n\n<p>To get more detailed information on the test result, you pass the <code>verbosity<\/code> argument with the value 2 to the <code>unittest.main()<\/code> function:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-10\" data-shcb-language-name=\"Python\" data-shcb-language-slug=\"python\"><span><code class=\"hljs language-python\"><span class=\"hljs-keyword\">import<\/span> unittest\n\n<span class=\"hljs-keyword\">from<\/span> square <span class=\"hljs-keyword\">import<\/span> Square\n\n\n<span class=\"hljs-class\"><span class=\"hljs-keyword\">class<\/span> <span class=\"hljs-title\">TestSquare<\/span><span class=\"hljs-params\">(unittest.TestCase)<\/span>:<\/span>\n    <span class=\"hljs-function\"><span class=\"hljs-keyword\">def<\/span> <span class=\"hljs-title\">test_area<\/span><span class=\"hljs-params\">(self)<\/span>:<\/span>\n        square = Square(<span class=\"hljs-number\">10<\/span>)\n        area = square.area()\n        self.assertEqual(area, <span class=\"hljs-number\">100<\/span>)\n\n\n<span class=\"hljs-keyword\">if<\/span> __name__ == <span class=\"hljs-string\">'__main__'<\/span>:\n    unittest.main(verbosity=<span class=\"hljs-number\">2<\/span>)<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-10\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">Python<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">python<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>If you run the test again:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-11\" data-shcb-language-name=\"Python\" data-shcb-language-slug=\"python\"><span><code class=\"hljs language-python\">python test_square.py<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-11\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">Python<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">python<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>you&#8217;ll get the detailed information:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-12\" data-shcb-language-name=\"plaintext\" data-shcb-language-slug=\"plaintext\"><span><code class=\"hljs language-plaintext\">test_area (__main__.TestSquare) ... ok\n\n----------------------------------------------------------------------\nRan 1 test in 0.001s\n\nOK<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-12\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">plaintext<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">plaintext<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>The output list the test case with the result ok this time instead of the dot (.)<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id='running-tests-without-calling-unittest-main-function'>Running tests without calling unittest.main() function <a href=\"#running-tests-without-calling-unittest-main-function\" class=\"anchor\" id=\"running-tests-without-calling-unittest-main-function\" title=\"Anchor for Running tests without calling unittest.main() function\">#<\/a><\/h2>\n\n\n\n<p>First, remove the <code>if<\/code> block that calls the <code>unittest.main()<\/code> function:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-13\" data-shcb-language-name=\"Python\" data-shcb-language-slug=\"python\"><span><code class=\"hljs language-python\"><span class=\"hljs-keyword\">import<\/span> unittest\n\n<span class=\"hljs-keyword\">from<\/span> square <span class=\"hljs-keyword\">import<\/span> Square\n\n\n<span class=\"hljs-class\"><span class=\"hljs-keyword\">class<\/span> <span class=\"hljs-title\">TestSquare<\/span><span class=\"hljs-params\">(unittest.TestCase)<\/span>:<\/span>\n    <span class=\"hljs-function\"><span class=\"hljs-keyword\">def<\/span> <span class=\"hljs-title\">test_area<\/span><span class=\"hljs-params\">(self)<\/span>:<\/span>\n        square = Square(<span class=\"hljs-number\">10<\/span>)\n        area = square.area()\n        self.assertEqual(area, <span class=\"hljs-number\">100<\/span>)<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-13\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">Python<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">python<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>Second, execute the following command to run the test:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-14\" data-shcb-language-name=\"Python\" data-shcb-language-slug=\"python\"><span><code class=\"hljs language-python\">python3 -m unittest<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-14\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">Python<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">python<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>This command discovers all the test classes whose names start with <code>Test*<\/code> located in the <code>test_*<\/code> file and execute the test methods that start with <code>test*<\/code>.  the <code>-m<\/code>  option stands for the module.<\/p>\n\n\n\n<p>In this example, the command executes the <code>test_area()<\/code> method of the <code>TestSquare<\/code> class in the <code>test_square.py<\/code> test module.<\/p>\n\n\n\n<p>If you use macOS or Linux, you need to use the <code>python3<\/code> command instead:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-15\" data-shcb-language-name=\"Python\" data-shcb-language-slug=\"python\"><span><code class=\"hljs language-python\">python3 -m unittest<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-15\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">Python<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">python<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>It&#8217;ll return something like:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-16\" data-shcb-language-name=\"Python\" data-shcb-language-slug=\"python\"><span><code class=\"hljs language-python\">.\n----------------------------------------------------------------------\nRan <span class=\"hljs-number\">1<\/span> test <span class=\"hljs-keyword\">in<\/span> <span class=\"hljs-number\">0.000<\/span>s\n\nOK<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-16\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">Python<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">python<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>To display more information, you can add <code>-v<\/code> option to the above command. <code>v<\/code> stands for verbosity. It&#8217;s like calling the unittest.<code>main()<\/code> with verbosity argument with value 2.<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-17\" data-shcb-language-name=\"Python\" data-shcb-language-slug=\"python\"><span><code class=\"hljs language-python\">python -m unittest -v<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-17\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">Python<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">python<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>Output:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-18\" data-shcb-language-name=\"Python\" data-shcb-language-slug=\"python\"><span><code class=\"hljs language-python\">test_area (test_square.TestSquare) ... ok\n \n\n----------------------------------------------------------------------\nRan <span class=\"hljs-number\">1<\/span> tests <span class=\"hljs-keyword\">in<\/span> <span class=\"hljs-number\">0.000<\/span>s\n\nOK<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-18\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">Python<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">python<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<h2 class=\"wp-block-heading\" id='testing-expected-exceptions'>Testing expected exceptions <a href=\"#testing-expected-exceptions\" class=\"anchor\" id=\"testing-expected-exceptions\" title=\"Anchor for Testing expected exceptions\">#<\/a><\/h2>\n\n\n\n<p>The <code>Square<\/code> constructor accepts a <code>length<\/code> parameter. The <code>length<\/code> parameter should be either an <code>int<\/code> or <code>float<\/code>. If you pass the value that is not in these types, the <code>Square<\/code> constructor should <a href=\"https:\/\/www.pythontutorial.net\/python-oop\/python-raise-exception\/\">raise<\/a> a <code>TypeError<\/code> exception.<\/p>\n\n\n\n<p>To test if the <code>Square<\/code> constructor raises the <code>TypeError<\/code> exception, you use the <code>assertRaises()<\/code> method in a <a href=\"https:\/\/www.pythontutorial.net\/advanced-python\/python-context-managers\/\">context manager<\/a> like this:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-19\" data-shcb-language-name=\"Python\" data-shcb-language-slug=\"python\"><span><code class=\"hljs language-python\"><span class=\"hljs-keyword\">import<\/span> unittest\n\n<span class=\"hljs-keyword\">from<\/span> square <span class=\"hljs-keyword\">import<\/span> Square\n\n\n<span class=\"hljs-class\"><span class=\"hljs-keyword\">class<\/span> <span class=\"hljs-title\">TestSquare<\/span><span class=\"hljs-params\">(unittest.TestCase)<\/span>:<\/span>\n    <span class=\"hljs-function\"><span class=\"hljs-keyword\">def<\/span> <span class=\"hljs-title\">test_area<\/span><span class=\"hljs-params\">(self)<\/span>:<\/span>\n        square = Square(<span class=\"hljs-number\">10<\/span>)\n        area = square.area()\n        self.assertEqual(area, <span class=\"hljs-number\">100<\/span>)\n\n    <span class=\"hljs-function\"><span class=\"hljs-keyword\">def<\/span> <span class=\"hljs-title\">test_length_with_wrong_type<\/span><span class=\"hljs-params\">(self)<\/span>:<\/span>\n        <span class=\"hljs-keyword\">with<\/span> self.assertRaises(TypeError):\n            square = Square(<span class=\"hljs-string\">'10'<\/span>)<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-19\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">Python<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">python<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>If you run the test again, it will fail:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-20\" data-shcb-language-name=\"Python\" data-shcb-language-slug=\"python\"><span><code class=\"hljs language-python\">python -m unittest -v<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-20\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">Python<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">python<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>Output:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-21\" data-shcb-language-name=\"plaintext\" data-shcb-language-slug=\"plaintext\"><span><code class=\"hljs language-plaintext\">test_area (test_square.TestSquare) ... ok\ntest_length_with_wrong_type (test_square.TestSquare) ... FAIL\n\n======================================================================\nFAIL: test_length_with_wrong_type (test_square.TestSquare)\n----------------------------------------------------------------------\nTraceback (most recent call last):\n  File \"D:\\python-unit-testing\\test_square.py\", line 13, in test_length_with_wrong_type\n    with self.assertRaises(TypeError):\nAssertionError: TypeError not raised\n\n----------------------------------------------------------------------\nRan 2 tests in 0.001s<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-21\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">plaintext<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">plaintext<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>The <code>test_length_with_wrong_type()<\/code> method expected that the <code>Square<\/code> constructor raises a <code>TypeError<\/code> exception. However, it didn&#8217;t. <\/p>\n\n\n\n<p>To pass the test, you need to raise an exception if the type of the <code>length<\/code> property is not <code>int<\/code> or <code>float<\/code> in the <code>Square<\/code> constructor:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-22\" data-shcb-language-name=\"Python\" data-shcb-language-slug=\"python\"><span><code class=\"hljs language-python\"><span class=\"hljs-class\"><span class=\"hljs-keyword\">class<\/span> <span class=\"hljs-title\">Square<\/span>:<\/span>\n    <span class=\"hljs-function\"><span class=\"hljs-keyword\">def<\/span> <span class=\"hljs-title\">__init__<\/span><span class=\"hljs-params\">(self, length)<\/span> -&gt; <span class=\"hljs-keyword\">None<\/span>:<\/span>\n        <span class=\"hljs-keyword\">if<\/span> type(length) <span class=\"hljs-keyword\">not<\/span> <span class=\"hljs-keyword\">in<\/span> &#91;int, float]:\n            <span class=\"hljs-keyword\">raise<\/span> TypeError(<span class=\"hljs-string\">'Length must be an integer or float'<\/span>)\n\n        self.length = length\n\n    <span class=\"hljs-function\"><span class=\"hljs-keyword\">def<\/span> <span class=\"hljs-title\">area<\/span><span class=\"hljs-params\">(self)<\/span>:<\/span>\n        <span class=\"hljs-keyword\">return<\/span> self.length * self.length<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-22\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">Python<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">python<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>Now, all the tests pass:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-23\" data-shcb-language-name=\"Python\" data-shcb-language-slug=\"python\"><span><code class=\"hljs language-python\">python -m unittest -v<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-23\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">Python<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">python<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>Output:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-24\" data-shcb-language-name=\"Python\" data-shcb-language-slug=\"python\"><span><code class=\"hljs language-python\">test_area (test_square.TestSquare) ... ok\ntest_length_with_wrong_type (test_square.TestSquare) ... ok\n\n----------------------------------------------------------------------\nRan <span class=\"hljs-number\">2<\/span> tests <span class=\"hljs-keyword\">in<\/span> <span class=\"hljs-number\">0.001<\/span>s\n\nOK<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-24\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">Python<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">python<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>The following example adds a test that expects a <code>ValueError<\/code> exception if the <code>length<\/code> is zero or negative:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-25\" data-shcb-language-name=\"Python\" data-shcb-language-slug=\"python\"><span><code class=\"hljs language-python\"><span class=\"hljs-keyword\">import<\/span> unittest\n\n<span class=\"hljs-keyword\">from<\/span> square <span class=\"hljs-keyword\">import<\/span> Square\n\n\n<span class=\"hljs-class\"><span class=\"hljs-keyword\">class<\/span> <span class=\"hljs-title\">TestSquare<\/span><span class=\"hljs-params\">(unittest.TestCase)<\/span>:<\/span>\n    <span class=\"hljs-function\"><span class=\"hljs-keyword\">def<\/span> <span class=\"hljs-title\">test_area<\/span><span class=\"hljs-params\">(self)<\/span>:<\/span>\n        square = Square(<span class=\"hljs-number\">10<\/span>)\n        area = square.area()\n        self.assertEqual(area, <span class=\"hljs-number\">100<\/span>)\n\n    <span class=\"hljs-function\"><span class=\"hljs-keyword\">def<\/span> <span class=\"hljs-title\">test_length_with_wrong_type<\/span><span class=\"hljs-params\">(self)<\/span>:<\/span>\n        <span class=\"hljs-keyword\">with<\/span> self.assertRaises(TypeError):\n            square = Square(<span class=\"hljs-string\">'10'<\/span>)\n\n    <span class=\"hljs-function\"><span class=\"hljs-keyword\">def<\/span> <span class=\"hljs-title\">test_length_with_zero_or_negative<\/span><span class=\"hljs-params\">(self)<\/span>:<\/span>\n        <span class=\"hljs-keyword\">with<\/span> self.assertRaises(ValueError):\n            square = Square(<span class=\"hljs-number\">0<\/span>)\n            square = Square(<span class=\"hljs-number\">-1<\/span>)<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-25\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">Python<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">python<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>If you run the test, it&#8217;ll fail:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-26\" data-shcb-language-name=\"Python\" data-shcb-language-slug=\"python\"><span><code class=\"hljs language-python\">python -m unittest -v<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-26\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">Python<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">python<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>Output:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-27\" data-shcb-language-name=\"Python\" data-shcb-language-slug=\"python\"><span><code class=\"hljs language-python\">test_area (test_square.TestSquare) ... ok\ntest_length_with_wrong_type (test_square.TestSquare) ... ok\ntest_length_with_zero_or_negative (test_square.TestSquare) ... FAIL\n\n======================================================================\nFAIL: test_length_with_zero_or_negative (test_square.TestSquare)\n----------------------------------------------------------------------\nTraceback (most recent call last):\n  File <span class=\"hljs-string\">\"D:\\python-unit-testing\\test_square.py\"<\/span>, line <span class=\"hljs-number\">17<\/span>, <span class=\"hljs-keyword\">in<\/span> test_length_with_zero_or_negative\n    <span class=\"hljs-keyword\">with<\/span> self.assertRaises(ValueError):\nAssertionError: ValueError <span class=\"hljs-keyword\">not<\/span> raised\n\n----------------------------------------------------------------------\nRan <span class=\"hljs-number\">3<\/span> tests <span class=\"hljs-keyword\">in<\/span> <span class=\"hljs-number\">0.001<\/span>s\n\nFAILED (failures=<span class=\"hljs-number\">1<\/span>)<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-27\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">Python<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">python<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>To make the test pass, you add another check to the <code>Square()<\/code> constructor:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-28\" data-shcb-language-name=\"Python\" data-shcb-language-slug=\"python\"><span><code class=\"hljs language-python\"><span class=\"hljs-class\"><span class=\"hljs-keyword\">class<\/span> <span class=\"hljs-title\">Square<\/span>:<\/span>\n    <span class=\"hljs-function\"><span class=\"hljs-keyword\">def<\/span> <span class=\"hljs-title\">__init__<\/span><span class=\"hljs-params\">(self, length)<\/span> -&gt; <span class=\"hljs-keyword\">None<\/span>:<\/span>\n        <span class=\"hljs-keyword\">if<\/span> type(length) <span class=\"hljs-keyword\">not<\/span> <span class=\"hljs-keyword\">in<\/span> &#91;int, float]:\n            <span class=\"hljs-keyword\">raise<\/span> TypeError(<span class=\"hljs-string\">'Length must be an integer or float'<\/span>)\n        <span class=\"hljs-keyword\">if<\/span> length &lt; <span class=\"hljs-number\">0<\/span>:\n            <span class=\"hljs-keyword\">raise<\/span> ValueError(<span class=\"hljs-string\">'Length must not be negative'<\/span>)\n\n        self.length = length\n\n    <span class=\"hljs-function\"><span class=\"hljs-keyword\">def<\/span> <span class=\"hljs-title\">area<\/span><span class=\"hljs-params\">(self)<\/span>:<\/span>\n        <span class=\"hljs-keyword\">return<\/span> self.length * self.length<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-28\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">Python<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">python<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>Now, all three tests pass:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-29\" data-shcb-language-name=\"Python\" data-shcb-language-slug=\"python\"><span><code class=\"hljs language-python\">python -m unittest -v<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-29\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">Python<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">python<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>Output:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-30\" data-shcb-language-name=\"plaintext\" data-shcb-language-slug=\"plaintext\"><span><code class=\"hljs language-plaintext\">test_area (test_square.TestSquare) ... ok\ntest_length_with_wrong_type (test_square.TestSquare) ... ok\ntest_length_with_zero_or_negative (test_square.TestSquare) ... ok     \n\n----------------------------------------------------------------------\nRan 3 tests in 0.001s\n\nOK<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-30\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">plaintext<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">plaintext<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<h2 class=\"wp-block-heading\" id='summary'>Summary <a href=\"#summary\" class=\"anchor\" id=\"summary\" title=\"Anchor for Summary\">#<\/a><\/h2>\n\n\n\n<ul class=\"wp-block-list\"><li>A unit test is an automated test that verifies a small piece of code, executes fast, and executes in an isolated manner.<\/li><li>Use the <code>unittest<\/code> module to perform unit testing.<\/li><li>Create a class that inherits from the <code>unittest.TestCase<\/code> class to make a test case.<\/li><li>Use the <code>assertEqual()<\/code> method to test if two values are equal. <\/li><li>Use the <code>assertRaises()<\/code> method in a context manager to test expected exceptions.<\/li><li>Use the <code>python -m unittest -v<\/code> command to run a test.<\/li><\/ul>\n<div class=\"helpful-block-content\" data-title=\"\">\n\t<header>\n\t\t<div class=\"wth-question\">Was this tutorial helpful ?<\/div>\n\t\t<div class=\"wth-thumbs\">\n\t\t\t<button\n\t\t\t\tdata-post=\"3557\"\n\t\t\t\tdata-post-url=\"https:\/\/www.pythontutorial.net\/python-unit-testing\/python-unittest\/\"\n\t\t\t\tdata-post-title=\"Python unittest\"\n\t\t\t\tdata-response=\"1\"\n\t\t\t\tclass=\"wth-btn-rounded wth-yes-btn\"\n\t\t\t>\n\t\t\t\t<svg\n\t\t\t\t\txmlns=\"http:\/\/www.w3.org\/2000\/svg\"\n\t\t\t\t\tviewBox=\"0 0 24 24\"\n\t\t\t\t\tfill=\"none\"\n\t\t\t\t\tstroke=\"currentColor\"\n\t\t\t\t\tstroke-width=\"2\"\n\t\t\t\t\tstroke-linecap=\"round\"\n\t\t\t\t\tstroke-linejoin=\"round\"\n\t\t\t\t\tclass=\"feather 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