A library for property-based testing

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  • License: Mozilla Public License 2.0 (MPL 2.0) (MPL-2.0)
  • Author: David R. MacIver and Zac Hatfield-Dodds
  • Tags python, testing, fuzzing, property-based-testing
  • Requires: Python >=3.9
  • Provides-Extra: cli, codemods, ghostwriter, pytz, dateutil, lark, numpy, pandas, pytest, dpcontracts, redis, crosshair, zoneinfo, django, watchdog, all
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Hypothesis

Hypothesis is the property-based testing library for Python. A property-based test asserts something for all inputs, and lets Hypothesis generate them — including inputs you may not have thought of.

from hypothesis import given, strategies as st


@given(st.lists(st.integers() | st.floats()))
def test_matches_builtin(ls):
    assert sorted(ls) == my_sort(ls)

Additionally, when a property fails, Hypothesis doesn't just report any failing example — it reports the simplest possible one. This makes property-based tests a powerful tool for debugging, as well as testing.

For instance,

def my_sort(ls):
    return list(reversed(sorted(ls, reverse=True)))

fails with:

Falsifying example: test_matches_builtin(ls=[0, math.nan])

Installation

To install Hypothesis:

pip install hypothesis

There are also optional extras available.

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