Testing in Python

testing
Python
Last reviewed

February 12, 2025

Last modified

April 11, 2025

In Python, two widely used testing frameworks are pytest and unittest. This guide focuses on pytest, which is recommended for its simplicity and readability. If you are new to testing in Python, pytest is a great starting point.

  • pytest is a third-party testing framework that is more user-friendly, requires less boilerplate, and offers better readability.
  • unittest is part of the Python standard library and follows a more traditional object-oriented style of writing tests.

Step 1. Setup a testing framework

Install pytest

pip install pytest

A good practice is to organize the codebase into a src directory for the source code and a tests directory for the test suite. For example:

src/
    mypkg/
        __init__.py
        add.py
        draw_random_number.py
tests/
    test_add.py
    test_draw_random_number.py
    ...

Step 2. Identify testable units

Identify functions, methods, or classes on your code that should be tested. Focus on critical computations and potential points of failure.

Step 3. Write test cases

Write test functions using pytest. Here’s an example:

# src/mypkg/add.py
def add(x,y):
    return x + y

# tests/test_add.py
from mypkg.add import add

def test_add():
    assert add(1, 2) == 3
    assert add(0, 0) == 0
    assert add(-1, -1) == -2
Tip

Limit the number of assert statements in a single test function. Otherwise, when a particular assert fails, the remaining assertions in the test function will not be executed.

Step 4. Run tests locally

Run all tests in the project by executing the following command:

pytest

Run a specific test file:

pytest tests/test_add.py

Step 5. Debug and fix failing tests

The test results displayed in the console will help you to identify any failures or errors. If errors occur, debug the failing tests by examining failure messages and stack traces.

Step 6. Run coverage report locally

Generate a coverage report to gain insights into which parts of the codebase have been executed during testing (see Code Coverage).

pip install pytest-cov
pytest --cov=mypkg tests/

Step 7. Automate testing with Continuous Integration

Integrate youre test suite with a Continuous Integration service (e.g., GitHub Actions) to run tests automatically on every code change.

Learning materials for automated testing

Examples of repositories with tests

Learn more