`unittest`

The Python unittest module provides a framework for creating and running unit tests, allowing developers to ensure their code behaves as expected.

It supports test automation, sharing setup and shutdown code for tests, aggregation of tests into collections, and independence of the tests from the reporting framework.

Here’s a quick example:

Python
      
>>> import unittest

>>> class TestSum(unittest.TestCase):
...     def test_sum(self):
...         self.assertEqual(sum([1, 2, 3]), 6)
...

>>> unittest.main(exit=False)

Key Features

Organizes tests into test suites
Supports test fixtures for setup and teardown operations
Provides automated test discovery capabilities
Includes a wide range of built-in assertions for verifying test results
Allows for test skipping, expected failures, and subtests
Enables running tests from the command line or programmatically
Integrates with test runners, continuous integration (CI) tools, and IDEs for comprehensive test reporting

Frequently Used Classes and Functions

Object	Type	Description
`unittest.TestCase`	Class	Serves as the base class for creating new test cases
`unittest.main()`	Function	Runs a set of tests as a command-line program
`unittest.TestCase.assertEqual()`	Method	Checks whether two objects are equal
`unittest.TestCase.setUp()`	Method	Prepares the test fixture before each test method runs
`unittest.TestCase.tearDown()`	Method	Cleans up after the test method runs
`unittest.TestLoader`	Class	Loads test cases from modules, classes, or test methods

Examples

Creating a test case:

Python
      
>>> import unittest

>>> class TestMax(unittest.TestCase):
...     def test_max(self):
...         self.assertEqual(max([1, 5, 3]), 5)
...

Using .setUp() and .tearDown() methods for test preparation and cleanup:

Python
      
        
      
    
>>> class TestExample(unittest.TestCase):
...     def setUp(self):
...         self.value = 5
...
...     def tearDown(self):
...         self.value = 0
...
...     def test_increment(self):
...         self.value += 1
...         self.assertEqual(self.value, 6)
...

Common Use Cases

Writing and organizing unit tests for functions and classes
Automating test runs with CI tools
Ensuring code changes do not break existing functionality
Documenting the expected behavior of code through test cases
Testing edge cases and error handling
Writing regression tests to prevent bugs from reappearing
Refactoring code confidently by ensuring all tests pass

Real-World Example

Say that you’re building a basic calculator and want to test it to ensure it works correctly. Here’s how you could use the unittest module to achieve this:

Python
      
        
      
    
>>> import unittest

>>> def add(a, b):
...     return a + b
...

>>> class TestCalculator(unittest.TestCase):
...     def test_add(self):
...         self.assertEqual(add(2, 3), 5)
...         self.assertEqual(add(-1, 1), 0)
...         self.assertEqual(add(-1, -1), -2)
...

>>> unittest.main(exit=False)

In this example, you use the unittest module to verify that the add() function produces the expected results for different input values, ensuring reliability and correctness.

Tutorial

Python's unittest: Writing Unit Tests for Your Code

In this tutorial, you'll learn how to use the unittest framework to create unit tests for your Python code. Along the way, you'll also learn how to create test cases, fixtures, test suites, and more.

intermediate testing

For additional information on related topics, take a look at the following resources: