timothycrosley/hypothesis-auto

An extensions for Hypothesis that provides fully automatic testing for type hinted functions

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hypothesis-auto is an extension for the Hypothesis project that enables fully automatic tests for type annotated functions.

Key Features:

• Type Annotation Powered: Utilize your function's existing type annotations to build dozens of test cases automatically.
• Low Barrier: Start utilizing property-based testing in the lowest barrier way possible. Just run auto_test(FUNCTION) to run dozens of test.
• pytest Compatible: Like Hypothesis itself, hypothesis-auto has built-in compatibility with the popular pytest testing framework. This means that you can turn your automatically generated tests into individual pytest test cases with one line.
• Scales Up: As you find your self needing to customize your auto_test cases, you can easily utilize all the features of Hypothesis, including custom strategies per a parameter.

Installation:

To get started - install hypothesis-auto into your projects virtual environment:

pip3 install hypothesis-auto

OR

poetry add hypothesis-auto

OR

pipenv install hypothesis-auto

Usage Examples:

!!! warning In old usage examples you will see _ prefixed parameters like _auto_verify=. This was done to avoid conflicting with existing function parameters. Based on community feedback the project switched to _ suffixes, such as auto_verify_= to keep the likely hood of conflicting low while avoiding the connotation of private parameters.

Framework independent usage

Basic auto_test usage:

from hypothesis_auto import auto_test


def add(number_1: int, number_2: int = 1) -> int:
    return number_1 + number_2


auto_test(add)  # 50 property based scenarios are generated and ran against add
auto_test(add, auto_runs_=1_000)  # Let's make that 1,000

Adding an allowed exception:

from hypothesis_auto import auto_test


def divide(number_1: int, number_2: int) -> int:
    return number_1 / number_2

auto_test(divide)

-> 1012                     raise the_error_hypothesis_found
   1013
   1014         for attrib in dir(test):

<ipython-input-2-65a3aa66e9f9> in divide(number_1, number_2)
      1 def divide(number_1: int, number_2: int) -> int:
----> 2     return number_1 / number_2
      3

0/0

ZeroDivisionError: division by zero


auto_test(divide, auto_allow_exceptions_=(ZeroDivisionError, ))

Using auto_test with a custom verification method:

from hypothesis_auto import Scenario, auto_test


def add(number_1: int, number_2: int = 1) -> int:
    return number_1 + number_2


def my_custom_verifier(scenario: Scenario):
    if scenario.kwargs["number_1"] > 0 and scenario.kwargs["number_2"] > 0:
        assert scenario.result > scenario.kwargs["number_1"]
        assert scenario.result > scenario.kwargs["number_2"]
    elif scenario.kwargs["number_1"] < 0 and scenario.kwargs["number_2"] < 0:
        assert scenario.result < scenario.kwargs["number_1"]
        assert scenario.result < scenario.kwargs["number_2"]
    else:
        assert scenario.result >= min(scenario.kwargs.values())
        assert scenario.result <= max(scenario.kwargs.values())


auto_test(add, auto_verify_=my_custom_verifier)

Custom verification methods should take a single Scenario and raise an exception to signify errors.

For the full set of parameters, you can pass into auto_test see its API reference documentation.

pytest usage

Using auto_pytest_magic to auto-generate dozens of pytest test cases:

from hypothesis_auto import auto_pytest_magic


def add(number_1: int, number_2: int = 1) -> int:
    return number_1 + number_2


auto_pytest_magic(add)

Using auto_pytest to run dozens of test case within a temporary directory:

from hypothesis_auto import auto_pytest


def add(number_1: int, number_2: int = 1) -> int:
    return number_1 + number_2


@auto_pytest()
def test_add(test_case, tmpdir):
    tmpdir.mkdir().chdir()
    test_case()

Using auto_pytest_magic with a custom verification method:

from hypothesis_auto import Scenario, auto_pytest


def add(number_1: int, number_2: int = 1) -> int:
    return number_1 + number_2


def my_custom_verifier(scenario: Scenario):
    if scenario.kwargs["number_1"] > 0 and scenario.kwargs["number_2"] > 0:
        assert scenario.result > scenario.kwargs["number_1"]
        assert scenario.result > scenario.kwargs["number_2"]
    elif scenario.kwargs["number_1"] < 0 and scenario.kwargs["number_2"] < 0:
        assert scenario.result < scenario.kwargs["number_1"]
        assert scenario.result < scenario.kwargs["number_2"]
    else:
        assert scenario.result >= min(scenario.kwargs.values())
        assert scenario.result <= max(scenario.kwargs.values())


auto_pytest_magic(add, auto_verify_=my_custom_verifier)

Custom verification methods should take a single Scenario and raise an exception to signify errors.

For the full reference of the pytest integration API see the API reference documentation.

Why Create hypothesis-auto?

I wanted a no/low resistance way to start incorporating property-based tests across my projects. Such a solution that also encouraged the use of type hints was a win/win for me.

I hope you too find hypothesis-auto useful!

~Timothy Crosley