Using a TestCase subclass in another unit test in Python

Question

Here's an example:

from unittest import TestCase


class DogTest(TestCase):

    def create_dog(self, weight):

        dog = {'weight': weight}

        return dog


class DogPawTest(TestCase):

    def test_dog_paw(self):

        dog_test = DogTest()
        dog = dog_test.create_dog(weight=10)
        self.assertEqual(dog['weight'], 10)

It throws

ValueError: no such test method in <class 'unittest_case_import.DogTest'>: runTest

Test cases should be independent. Also, create_dog can and should be outside of the test class. Changing the definition to DogTest(object) solves the riddle. But I have a case where it's not an option.

How can I use the methods of another TestCase-based class in test_dog_paw?

you can use DogPawTest(DogTest) in DogPawTest. and use self.create_dog(weight=10 — Manoj Jadhav
– Manoj Jadhav, Commented Dec 18, 2017 at 9:21
@ManojJadhav Alas, in my case I have to import multiple TestCase classes within a single class. Mixins may help, but it'd involve much refactoring. — Anton Tarasenko
– Anton Tarasenko, Commented Dec 18, 2017 at 9:29

Doddie · Accepted Answer · 2017-12-18 12:20:16Z

1

With the example you have provided I don't see any need for inheritance. You could just as easily do something like:

from unittest import TestCase

def create_dog(weight):
    return {'weight': weight}

class DogTest(TestCase):
    def test_dogs(self):
        heavy_dog = create_dog(25)
        ...

class DogPawTest(TestCase):
    def test_dog_paw(self):
        dog = create_dog(weight=10)
        self.assertEqual(dog['weight'], 10)

It could also be worth having a look at something like PyTest's fixtures. That might change this code to be something like:

from unittest import TestCase
import pytest

@pytest.fixture
def dog():
    """Just your regular average dog"""
    return {'weight': 15}

@pytest.fixture
def heavy_dog():
    return {'weight': 30}

@pytest.fixture
def light_dog():
    return {'weight': 10}

class DogTest(TestCase):
    def test_dogs(self, heavy_dog):
        ...

class DogPawTest(TestCase):
    def test_dog_paw(self, dog):
        self.assertEqual(dog['weight'], 10)

answered Dec 18, 2017 at 12:20

Doddie

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2 Comments

Anton Tarasenko Over a year ago

Thank you! I have the code that forces me to inherit, so I was looking for short ways to create an instance of an established test case.

Doddie Over a year ago

Well, my answer is not really applicable then I guess.

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