Quick Tutorial: Introduction to Unit Testing in Python

🧪 Quick Tutorial: Introduction to Unit Testing in Python

Testing is one of the most essential parts of professional programming. It ensures that your code runs correctly — not just once, but every time it’s changed or updated.

At AI Computer Classes – Indore, we focus on teaching practical coding workflows that make you a reliable and efficient developer. One such workflow is unit testing — an essential skill for any Python programmer in 2025 and beyond.

Let’s dive into a beginner-friendly, hands-on guide to unit testing in Python and see how you can use it to make your code cleaner, more reliable, and easier to maintain.

🧩 What is Unit Testing?

Unit testing is a process where you test small parts (or units) of your code — usually individual functions or classes — to make sure they work as expected.

Imagine you wrote a function that calculates discounts. Before integrating it into your full project, you can test that one function independently.

💡 Example:

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

# Expected Output: 5
print(add(2, 3))

Here, testing means checking if add(2, 3) really returns 5.

In real-world projects, you don’t do this manually — you use automated tests using Python’s built-in unittest module.

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⚙️ Why Unit Testing Matters

Unit testing isn’t just for big companies — it’s for every serious coder who wants to:

• ✅ Write error-free code
• ⚡ Catch bugs early
• 🔄 Simplify debugging
• 🧠 Improve logical thinking
• 💼 Build confidence before deployment

Think of it as a safety net for your code. Once tests pass, you know your logic is solid.

🧠 The Basics of Python’s unittest Module

Python comes with a built-in module called unittest that lets you write and run automated tests easily.

Here’s how a basic test file looks:

import unittest

def multiply(a, b):
    return a * b

class TestMultiply(unittest.TestCase):
    def test_positive_numbers(self):
        self.assertEqual(multiply(2, 3), 6)

    def test_negative_numbers(self):
        self.assertEqual(multiply(-2, 3), -6)

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

When you run this file, it will check both cases — if any test fails, you’ll immediately know which one and why.

🧩 Understanding Common Assertions

Assertions are the core of testing — they check if something is true.

Here are some commonly used ones:

AssertionPurposeExampleassertEqual(a, b)Checks if a == bassertEqual(2+2, 4)assertNotEqual(a, b)Checks if a != bassertNotEqual(3*3, 8)assertTrue(x)Checks if x is TrueassertTrue(5 > 1)assertFalse(x)Checks if x is FalseassertFalse(1 > 3)assertRaises(ErrorType)Checks if a function raises an errorassertRaises(ValueError)

These make your tests clear, readable, and powerful.

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🧰 How to Run Unit Tests in Python

Running tests is simple — you don’t need any special tool. Just type this command in your terminal:

python -m unittest test_file_name.py

If all your tests pass, you’ll see something like this:

..
----------------------------------------------------------------------
Ran 2 tests in 0.001s

OK

If a test fails, Python shows which one and why — helping you fix the exact issue quickly.

🔁 Example: Testing a Function from a Real Project

Let’s say you built a function to calculate discounts:

def calculate_discount(price, percent):
    if percent < 0 or percent > 100:
        raise ValueError("Invalid discount percentage")
    return price - (price * percent / 100)

Now test it like this:

import unittest
from discount import calculate_discount

class TestDiscount(unittest.TestCase):
    def test_valid_discount(self):
        self.assertEqual(calculate_discount(100, 10), 90)

    def test_invalid_discount(self):
        with self.assertRaises(ValueError):
            calculate_discount(100, 120)

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

That’s a real-world, professional way to test logic safely before deploying it to production.

📘 Tips for Writing Better Tests

1. Name Tests Clearly: Use descriptive names like test_user_login_valid instead of test1.
2. Test Edge Cases: Check for invalid inputs, empty lists, or zero values.
3. Keep Tests Independent: Each test should test only one thing.
4. Use Setup and Teardown: For reusable test setups, use setUp() and tearDown() methods.
5. Integrate with CI/CD: Tools like GitHub Actions can run tests automatically when you push code.

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🧭 Conclusion

Unit testing is not just a developer’s tool — it’s a confidence booster.

When you write tests, you don’t just check your code — you prove that it works.

At AI Computer Classes – Indore, our Programming & IT Development course includes:

• Real-world Python projects
• Automated testing workflows
• Integration with tools like Tally Prime, Power BI, and Flask

If you want to become a complete developer who writes clean, tested, and reliable code — start learning today!

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