Property-based tests for the Python standard library (and builtins)

Find and fix bugs in Python, before they ship to users.

CPython's existing test suite is good, but bugs still slip through occasionally. We think that using property-based testing tools - i.e. Hypothesis - can help with this. They're no magic bullet, but computer-assisted testing techniques routinely try inputs that humans wouldn't think of (or bother trying), and turn up bugs that humans missed.

Writing tests that describe every valid input often leads to tighter validation and cleaner designs too, even when no counterexamples are found!

We aim to have a compelling proof-of-concept by PyCon US, and be running as part of the CPython CI suite by the end of the sprints.

By contributing to this repository, you agree to license the contributed code under user's choice of the Mozilla Public License Version 2.0, and the Python Software Foundation License Version 2.

This dual-licence is intended to make it as easy as possible for the tests in this repository to be used upstream by the CPython project, other implementations of Python, and the Hypothesis project and ecosystem.

To run the tests against the current version of Python:

• pip install -r requirements.txt (or hypothesis hypothesmith)
• python -m unittest

For development, we use tox to manage an extensive suite of auto-formatters and linters, so:

• pip install tox
• tox

will set up a virtualenv for you, install everything, and finally run the formatters, linters, and test suite.

• Zac Hatfield-Dodds
• Paul Ganssle

Bugs found via this specific project:

• BPO-38953 tokenize.tokenize -> tokenize.untokenize does not round-trip as documented. Nor, for that matter, do the tokenize/untokenize functions in lib2to3.pgen.tokenize.