unittest Basics

Python includes a built-in testing framework called unittest.

It helps you write automated tests that run many checks quickly.

Instead of manually printing results, tests can verify code for you.

What Is unittest?

unittest is Python’s standard testing library.

It lets you:

• group tests
• compare expected results
• run many tests
• detect failures automatically

Why It Matters

With unittest, you can test code again after changes and make sure old features still work.

Basic Example

Create a file:

test_math.py

Add:

import unittest

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

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

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

Output Example

.
----------------------------------------------------------------------
Ran 1 test in 0.000s

OK

How It Works

Import unittest

import unittest

Loads the testing tools.

Create Test Class

class TestMath(unittest.TestCase):

Your test class inherits from unittest.TestCase.

Create Test Methods

Methods should start with:

test_

Example:

def test_add(self):

Use Assertions

self.assertEqual(add(2, 3), 5)

Checks actual result equals expected result.

Run Tests

unittest.main()

Runs all test methods.

Multiple Tests

import unittest

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

class TestMath(unittest.TestCase):
    def test_add_one(self):
        self.assertEqual(add(1, 1), 2)

    def test_add_two(self):
        self.assertEqual(add(0, 5), 5)

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

Output Example

..
----------------------------------------------------------------------
Ran 2 tests in 0.000s

OK

Each dot means one passing test.

Example Failure

self.assertEqual(add(2, 2), 5)

This test fails because the answer should be 4.

Code Along

Create function:

def square(n):
    return n * n

Write two unittest tests.

Mini Challenge

Create function:

def is_even(n):
    return n % 2 == 0

Write tests for:

• 2 → True
• 3 → False

Expected output:

..
OK

Real World Use Case

Developers use unittest for APIs, business rules, utilities, calculations, and backend systems.

Quiz

1. What is unittest?
2. What must test method names start with?
3. What does assertEqual() do?
4. What does unittest.main() do?

Assignment

Create a double(n) function and test it with three unittest test methods.

Summary

You learned how to use Python’s unittest module to create and run automated tests.