negating a custom unittest in python

Question

I've written a custom assertion to test if two lists of objects contain objects with the same attributes, and now I want to use the negation of the test to check if two lists are unequal.

from unittest import TestCase
from classes import *

class BaseTestCase(TestCase):
    def assertCountObjectsEqual(self, list1, list2):
        if len(list1) != len(list2):
            raise AssertionError("lists must be the same length")
        elif any(t1.__class__ != t2.__class__ or t1.__dict__ != t2.__dict__ for t1, t2 in zip(list1, list2)):
            raise AssertionError("objects are not the same")
        else:
            pass

The positive case works

class TestFillDemand(BaseTestCase):
    def test_fruit(self):
        self.assertCountObjectsEqual([Apple(), Apple(), Banana()], [Apple(), Apple(), Banana()])

But I want to be able to reuse the code for something like the following:

    def test_fruit_unequal(self):
        self.assertRaises(AssertionError, self.assertCountObjectsEqual([Apple(), Apple(), Banana()], [Apple(), Banana()]))

rather than having to redefine an assertCountObjectsUnequal method. Unfortunately the above code doesn't work.

Is there an easy way to do that?

alecxe · Accepted Answer · 2017-05-31 22:58:41Z

2

One option would be to wrap your list of objects into a custom "Collection" class defining the __eq__() magic method. This way, you will be able to utilize built-in assertion methods - assertEqual() and assertNotEqual():

from unittest import TestCase

class Apple:
    pass


class Banana:
    pass


class Collection:
    def __init__(self, objects):
        self.objects = objects

    def __eq__(self, other):
        if len(self.objects) != len(other.objects):
            return False
        if any(t1.__class__ != t2.__class__ or t1.__dict__ != t2.__dict__ for t1, t2 in zip(self.objects, other.objects)):
            return False

        return True


class BaseTestCase(TestCase):
    def test_fruit_equal(self):
        self.assertEqual(Collection([Apple(), Apple(), Banana()]), Collection([Apple(), Apple(), Banana()]))

    def test_fruit_unequal(self):
        self.assertNotEqual(Collection([Apple(), Apple(), Banana()]), Collection([Apple(), Banana()]))

Both tests pass.

answered May 31, 2017 at 22:58

alecxe

476k127 gold badges1.1k silver badges1.2k bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Allen Wang Over a year ago

This works, but I guess I wanted to know whether there was a way to negate a test, without having to define the "Not" version separately.

Collectives™ on Stack Overflow

negating a custom unittest in python

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related