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])
To install Hypothesis:
pip install hypothesis
There are also optional extras available.