Python Testing with unittest

In this page:

Introduction to Unit Testing
Writing Assertions
Testing Exceptions
Setup and Teardown Methods
Running unittest inside Script

Introduction to Unit Testing

Unit testing means writing code that automatically verifies individual pieces of your application -- functions or classes -- behave correctly, rather than manually re-checking behavior by hand every time you make a change. unittest is Python's built-in testing framework, modeled after the xUnit family found in many other languages.

Example: Introduction to Unit Testing

python

import unittest

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

class TestAdd(unittest.TestCase):
    def test_add(self):
        self.assertEqual(add(2, 3), 5)

unittest.main(argv=[""], exit=False)

Writing Assertions

Assertion methods like assertEqual(a, b) check that two values match and produce a clear, specific failure message naming both values if they don't -- more informative than a bare assert a == b, which only tells you the assertion failed without showing what the actual values were.

Example: Writing Assertions

python

import unittest

class TestMath(unittest.TestCase):
    def test_equal(self):
        self.assertEqual(2 + 2, 4)

unittest.main(argv=[""], exit=False)

Testing Exceptions

assertRaises() is used as a context manager to verify that a block of code raises a specific exception type when given invalid input, letting you test error-handling paths as rigorously as you test the normal success path.

Example: Testing Exceptions

python

import unittest

def divide(a, b):
    return a / b

class TestDivide(unittest.TestCase):
    def test_zero_division(self):
        with self.assertRaises(ZeroDivisionError):
            divide(1, 0)

unittest.main(argv=[""], exit=False)

Setup and Teardown Methods

setUp() runs automatically before every individual test method in a test class, and tearDown() runs automatically after each one -- the standard place to prepare shared fixtures (like mock files or database connections) and then clean them up, without repeating that setup code in every single test.

Example: Setup and Teardown Methods

python

import unittest

class TestExample(unittest.TestCase):
    def setUp(self):
        self.value = 10

    def test_value(self):
        self.assertEqual(self.value, 10)

unittest.main(argv=[""], exit=False)

Running unittest inside Script

Adding unittest.main() inside an if __name__ == __main__: guard lets you run all the tests in a file directly by executing that script, without needing to invoke a separate test-runner command -- convenient for quick, single-file test suites.

Example: Running unittest inside Script

python

import unittest

class TestBasic(unittest.TestCase):
    def test_true(self):
        self.assertTrue(1 == 1)

if __name__ == "__main__":
    unittest.main(argv=[""], exit=False)

🔒

Chapter Quiz — Complete all 15 topics to unlock

0/15 topics done

Complete these topics first:

← Previous Lesson Python Debugging Techniques Next Lesson → Python Common Mistakes

Python Testing with unittest

Introduction to Unit Testing

Writing Assertions

Testing Exceptions

Setup and Teardown Methods

Running unittest inside Script

Chapter Quiz — Complete all 15 topics to unlock

Login to run this code