26. Unit Testing with unittest

Level: AdvancedDuration: 32m

Why Unit Testing Matters

Unit tests check small, independent parts of your code (functions or classes) to ensure they work correctly. Writing tests helps catch bugs early, maintain code quality, and make future changes safer.

Getting Started with unittest

Python's `unittest` module is built-in and provides a framework to define and run tests easily.

python

import unittest

# Function to test
def add(a, b):
    return a + b

# Test case class
class TestMath(unittest.TestCase):
    def test_add(self):
        self.assertEqual(add(2, 3), 5)
        self.assertEqual(add(-1, 1), 0)

if __name__ == '__main__':
    unittest.main()

Here, `TestMath` is a test case class inheriting from `unittest.TestCase`. Each method starting with `test_` is a separate test.

Common Assertions

Assertions check if a condition holds true. Some common assertions include:

Assertion	Description
assertEqual(a, b)	Check a == b
assertNotEqual(a, b)	Check a != b
assertTrue(x)	Check x is True
assertFalse(x)	Check x is False
assertRaises(Exception, func, *args)	Check that an exception is raised

Setup and Teardown

Sometimes you need to prepare resources before tests and clean up after. Use `setUp()` and `tearDown()` methods.

python

class TestFiles(unittest.TestCase):
    def setUp(self):
        self.file = open('test.txt', 'w')

    def test_write(self):
        self.file.write('Hello')
        self.file.seek(0)
        self.assertEqual(self.file.read(), 'Hello')

    def tearDown(self):
        self.file.close()

💡 Always close resources in `tearDown()` to prevent side effects across tests.

Best Practices

Write tests for every function or class method.
Keep tests independent of each other.
Use descriptive test method names.
Test both normal and edge cases.
Run tests automatically when code changes (continuous integration).

Mini Project Step

Write a simple calculator module with functions for addition, subtraction, multiplication, and division. Create a `unittest` test suite to verify all operations, including division by zero handling.