You pick a testing framework when you start a project and rarely revisit the decision. Pick the wrong one and you end up refactoring your entire test suite six months later — or shipping bugs that your tests structurally cannot catch. In 2026, three frameworks dominate the Python testing landscape: unittest (standard library), pytest (ecosystem default), and hypothesis (property-based testing). Here is what each one actually does, where it falls short, and how to combine them effectively.
unittest: the built-in baseline
unittest ships with Python. No installation required. It follows the xUnit pattern: subclass TestCase, prefix methods with test_, and use self.assert* helpers.
import unittest
from myapp.auth import TokenValidator, TokenExpiredError
