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Testing in Python for Beginners. Using `unittest` and `pytest` with Fun Examples

· 2 min read
Serhii Hrekov
Serhii Hrekov
software engineer, creator, artist, programmer, projects founder

Writing tests in Python helps ensure that your code works correctly. In this guide, we'll use two popular testing tools: the built-in unittest module and the third-party library pytest. We'll walk through both using examples related to vegetables and AI model names.

What Is Testing?​

Testing means checking that your code behaves as expected. Instead of manually running your program over and over, you write automated tests that run every time you make a change.

unittest — Python’s Built-in Testing Tool​

Let’s start with a simple example using vegetables.

Example: Testing a Function That Capitalizes Vegetables​

# veggie_tools.py

def capitalize_veggie(veggie):
    return veggie.capitalize()

Now, test it using unittest:

# test_veggie_tools.py

import unittest
from veggie_tools import capitalize_veggie

class TestVeggieTools(unittest.TestCase):
    def test_capitalize_veggie(self):
        self.assertEqual(capitalize_veggie("carrot"), "Carrot")
        self.assertEqual(capitalize_veggie("tomato"), "Tomato")

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

Run the test:

python test_veggie_tools.py

pytest — A More Powerful, Cleaner Tool​

pytest makes your tests shorter and easier to read.

# test_veggie_tools_pytest.py

from veggie_tools import capitalize_veggie

def test_capitalize_veggie():
    assert capitalize_veggie("cabbage") == "Cabbage"
    assert capitalize_veggie("spinach") == "Spinach"

Run with:

pytest test_veggie_tools_pytest.py

✅ pytest is simple: no need to write test classes.

Another Example: AI Model Validator​

Suppose you want to validate AI model names:

# ai_model.py

def is_valid_model(name):
    return name in ["GPT-4", "Claude-3", "Gemini", "LLaMA"]

unittest Version​

# test_ai_model.py

import unittest
from ai_model import is_valid_model

class TestAIModel(unittest.TestCase):
    def test_is_valid_model(self):
        self.assertTrue(is_valid_model("GPT-4"))
        self.assertFalse(is_valid_model("GPT-2"))

pytest Version​

# test_ai_model_pytest.py

from ai_model import is_valid_model

def test_is_valid_model():
    assert is_valid_model("Claude-3")
    assert not is_valid_model("BERT")

When to Use What​

ToolProsUse if...
unittestComes with Python, matureYou don’t want extra dependencies
pytestCleaner syntax, powerful featuresYou want to write lots of tests fast

Summary​

  • Start with unittest — it’s simple and built-in.
  • Switch to pytest when you want more powerful features and cleaner tests.
  • Use real-world examples (vegetables, AI models) to make testing more fun!

Further Reading​