Hypothesis#

Hypothesis is a library that allows you to write tests that are parameterised from a source of examples. Then simple and comprehensible examples are generated, which can be used to fail your tests and to find errors with little effort.

Example#

To test lists with floating point numbers, many examples are tried, but only a simple example is given in the report for each bug (unique exception type and position):

[1]:

from hypothesis import given
from hypothesis.strategies import lists, floats

[2]:

# Add ipython magics
import ipytest
import pytest


ipytest.autoconfig()

[3]:

%%ipytest

@given(lists(floats(allow_nan=False, allow_infinity=False), min_size=1))
def test_mean(ls):
    mean = sum(ls) / len(ls)
    assert min(ls) <= mean <= max(ls)

F                                                                                            [100%]
============================================= FAILURES =============================================
____________________________________________ test_mean _____________________________________________

    @given(lists(floats(allow_nan=False, allow_infinity=False), min_size=1))
>   def test_mean(ls):

/tmp/ipykernel_8817/1742712940.py:2:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

ls = [9.9792015476736e+291, 1.7976931348623157e+308]

    @given(lists(floats(allow_nan=False, allow_infinity=False), min_size=1))
    def test_mean(ls):
        mean = sum(ls) / len(ls)
>       assert min(ls) <= mean <= max(ls)
E       assert inf <= 1.7976931348623157e+308
E        +  where 1.7976931348623157e+308 = max([9.9792015476736e+291, 1.7976931348623157e+308])
E       Falsifying example: test_mean(
E           ls=[9.9792015476736e+291, 1.7976931348623157e+308],
E       )

/tmp/ipykernel_8817/1742712940.py:4: AssertionError
========================================= warnings summary =========================================
../../../../../../.local/share/virtualenvs/python-311-6zxVKbDJ/lib/python3.11/site-packages/_pytest/config/__init__.py:1204
  /Users/veit/.local/share/virtualenvs/python-311-6zxVKbDJ/lib/python3.11/site-packages/_pytest/config/__init__.py:1204: PytestAssertRewriteWarning: Module already imported so cannot be rewritten: hypothesis
    self._mark_plugins_for_rewrite(hook)

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
===================================== short test summary info ======================================
FAILED t_97777e739d3141398e41c86d782e924f.py::test_mean - assert inf <= 1.7976931348623157e+308
1 failed, 1 warning in 0.63s

Installation#

$ pipenv install hypothesis

Alternatively, Hypothesis can also be installed with extras, for example

$ pipenv install hypothesis"[numpy, pandas]"

Note:

If you haven’t installed pipenv yet, you can find instructions on how to do this in Install pipenv.

See also:

Hypothesis for the Scientific Stack