Pytest: How to Use It (Beginner’s Guide with Examples)

If you're writing tests in Python, pytest is one of the most powerful, easy-to-use testing frameworks available. Whether you're a beginner or switching from unittest, this guide will show you how to use pytest effectively — with simple examples and best practices.

🐍 What Is Pytest?

Pytest is a testing framework for Python that allows you to write simple unit tests, complex functional tests, and even parameterized tests with very little boilerplate.

✅ Why Use Pytest?

• Super simple syntax
• Supports fixtures, parametrize, and plugins
• Works with any Python codebase
• Auto-discovers test files and functions

📦 How to Install Pytest

Install it via pip:

pip install pytest

Check version:

pytest --version

🧪 Writing Your First Test

test_math.py

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

def test_add():
    assert add(2, 3) == 5

That’s it! No class, no main function — just a plain function starting with test_.

🚀 How to Run Pytest

Just run this command in your terminal:

pytest

Pytest will automatically discover:

• Files starting with test_ or ending with _test.py
• Functions starting with test_

To run a specific file:

pytest test_math.py

To run a specific function:

pytest test_math.py::test_add

🔁 Example: Testing with Multiple Inputs

import pytest

@pytest.mark.parametrize("a, b, expected", [
    (1, 1, 2),
    (2, 3, 5),
    (10, -5, 5)
])
def test_add(a, b, expected):
    assert a + b == expected

🔧 Pytest Fixtures

Fixtures help you set up resources for your tests (like DB connections, configs, etc.)

import pytest

@pytest.fixture
def sample_data():
    return [1, 2, 3]

def test_length(sample_data):
    assert len(sample_data) == 3

❌ Handling Exceptions

import pytest

def divide(x, y):
    return x / y

def test_divide_by_zero():
    with pytest.raises(ZeroDivisionError):
        divide(1, 0)

📄 Generating Test Reports

Want a nice terminal report?

pytest -v

Generate an HTML report (with plugin):

pip install pytest-html
pytest --html=report.html

📝 Summary

Using pytest is simple and powerful. With just a few lines of code, you can test your Python functions, scale to more complex projects, and integrate with CI/CD pipelines.

✅ Quick Recap: