quick.py

Quick.py is a property-based testing library for Python inspired by the Haskell library QuickCheck. The core idea of QuickCheck is that instead of enumerating expected input and output for unit tests, you write properties about your function that should hold true for all inputs. This lets you write concise, powerful tests.

Installation

pip install quick.py

Examples

Basic example:

# example.py
from quick.features import QuickCheck

qc = QuickCheck(max_count=100)


@qc.forall('Associative property of addition for integers')
def prop(x: int, y: int):
    return (x + y) == (y + x)


TestAddtion = qc.as_testcase()

>>> nosetests example.py
....................................................................................................
----------------------------------------------------------------------
Ran 100 tests in 0.061s

OK

Custom generators:

# example.py
from quick.features import QuickCheck
from quick.generators import number
from quick.arbitrary import A

qc = QuickCheck(max_count=100)


def non_empty_list(el: number, ls: [number]):
    """
    Generator which always returns non empty list
    """
    ls.append(el)
    return ls


@qc.forall('The first element of a sorted list should be always lesser or eq than the last')
def prop(x: non_empty_list):
    sorted_x = sorted(x)
    first = sorted_x[0]
    last = sorted_x[-1]
    return first <= last


TestSort = qc.as_testcase()

>>> nosetests example.py
....................................................................................................
----------------------------------------------------------------------
Ran 100 tests in 0.070s

OK

Features

• Integration with unittests library
• Custom generators
• Simplification/Shrinking of failure input (in progress)

Controlled Randomness

def working_time(a: A):
    day = a.choose_one('Monday', 'Tuesday', 'Wednesday', 'Thursday')
    hour = a.choose(8, 17)
    return {'day': day, 'hour': hour}

Custom object generators

class User(object):

    def __init__(self, name, age):
        self.name = name
        self.age = age


def user_gen(name: str, a: A):
    age = a.choose(18, 100)
    return User(name, age)


@forall('Valid users')
def prop(user: user_gen):
    return ...

Shrinking

TBD, It's a trial implementation, and has limited functionalities yet.

Python 2 support?

Oups, sorry

Getting Help

For feature requests and bug reports submit an issue to the GitHub issue tracker for quick.py.